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 $231.44   4.456%   $241.753   $241.75   $241.75   $241.80  
  Purchase #2 $59.28   8.725%   $64.4522   $64.45   $64.45   $64.50  
  Purchase #3 $109.99   7.167%   $117.873   $117.87   $117.85   $117.90  
  Purchase #4 $149.36   12.746%   $168.3974   $168.40   $168.40   $168.40  
  Purchase #5 $147.84   12.197%   $165.872   $165.87   $165.85   $165.90  
  Purchase #6 $80.70   12.598%   $90.8666   $90.87   $90.85   $90.90  
  Purchase #7 $200.38   6.701%   $213.8075   $213.81   $213.80   $213.80  
  7 purchase totals = $978.99       $1,063.0217   $1,063.02   $1,062.95   $1,063.20