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 $116.73   6.166%   $123.9276   $123.93   $123.95   $123.90  
  Purchase #2 $245.68   12.776%   $277.0681   $277.07   $277.05   $277.10  
  Purchase #3 $180.89   5.445%   $190.7395   $190.74   $190.75   $190.70  
  Purchase #4 $138.90   12.237%   $155.8972   $155.90   $155.90   $155.90  
  Purchase #5 $173.35   6.587%   $184.7686   $184.77   $184.75   $184.80  
  Purchase #6 $178.59   12.663%   $201.2049   $201.20   $201.20   $201.20  
  Purchase #7 $95.69   6.757%   $102.1558   $102.16   $102.15   $102.20  
  7 purchase totals = $1,129.83       $1,235.7617   $1,235.77   $1,235.75   $1,235.80