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 $63.62   4.261%   $66.3308   $66.33   $66.35   $66.30  
  Purchase #2 $198.49   6.350%   $211.0941   $211.09   $211.10   $211.10  
  Purchase #3 $203.40   3.557%   $210.6349   $210.63   $210.65   $210.60  
  Purchase #4 $18.56   5.729%   $19.6233   $19.62   $19.60   $19.60  
  Purchase #5 $199.51   12.276%   $224.0018   $224.00   $224.00   $224.00  
  Purchase #6 $77.60   12.855%   $87.5755   $87.58   $87.60   $87.60  
  Purchase #7 $199.69   12.774%   $225.1984   $225.20   $225.20   $225.20  
  7 purchase totals = $960.87       $1,044.4588   $1,044.45   $1,044.50   $1,044.40