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 $39.28   12.378%   $44.1421   $44.14   $44.15   $44.10  
  Purchase #2 $193.71   4.820%   $203.0468   $203.05   $203.05   $203.00  
  Purchase #3 $201.60   3.506%   $208.6681   $208.67   $208.65   $208.70  
  Purchase #4 $71.88   9.578%   $78.7647   $78.76   $78.75   $78.80  
  Purchase #5 $248.58   6.276%   $264.1809   $264.18   $264.20   $264.20  
  Purchase #6 $118.28   12.257%   $132.7776   $132.78   $132.80   $132.80  
  Purchase #7 $25.86   6.809%   $27.6208   $27.62   $27.60   $27.60  
  7 purchase totals = $899.19       $959.2010   $959.20   $959.20   $959.20