Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $116.74   5.159%   $122.7626   $122.76   $122.75   $122.80  
  Purchase #2 $206.76   12.789%   $233.2025   $233.20   $233.20   $233.20  
  Purchase #3 $122.91   10.381%   $135.6693   $135.67   $135.65   $135.70  
  Purchase #4 $138.67   3.645%   $143.7245   $143.72   $143.70   $143.70  
  Purchase #5 $250.39   7.114%   $268.2027   $268.20   $268.20   $268.20  
  Purchase #6 $139.68   10.139%   $153.8422   $153.84   $153.85   $153.80  
  Purchase #7 $165.28   5.811%   $174.8844   $174.88   $174.90   $174.90  
  7 purchase totals = $1,140.43       $1,232.2882   $1,232.27   $1,232.25   $1,232.30