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 $190.93   9.852%   $209.7404   $209.74   $209.75   $209.70  
  Purchase #2 $55.48   9.825%   $60.9309   $60.93   $60.95   $60.90  
  Purchase #3 $227.25   13.131%   $257.0902   $257.09   $257.10   $257.10  
  Purchase #4 $59.77   6.424%   $63.6096   $63.61   $63.60   $63.60  
  Purchase #5 $80.67   5.743%   $85.3029   $85.30   $85.30   $85.30  
  Purchase #6 $140.94   6.648%   $150.3097   $150.31   $150.30   $150.30  
  Purchase #7 $31.39   11.791%   $35.0912   $35.09   $35.10   $35.10  
  7 purchase totals = $786.43       $862.0749   $862.07   $862.10   $862.00