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 $92.72   3.731%   $96.1794   $96.18   $96.20   $96.20  
  Purchase #2 $134.60   12.242%   $151.0777   $151.08   $151.10   $151.10  
  Purchase #3 $60.76   9.721%   $66.6665   $66.67   $66.65   $66.70  
  Purchase #4 $152.75   13.724%   $173.7134   $173.71   $173.70   $173.70  
  Purchase #5 $173.83   6.179%   $184.571   $184.57   $184.55   $184.60  
  Purchase #6 $132.42   7.341%   $142.141   $142.14   $142.15   $142.10  
  Purchase #7 $65.26   11.746%   $72.9254   $72.93   $72.95   $72.90  
  7 purchase totals = $812.34       $887.2744   $887.28   $887.30   $887.30