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 $234.71   12.462%   $263.9596   $263.96   $263.95   $264.00  
  Purchase #2 $144.61   11.552%   $161.3153   $161.32   $161.30   $161.30  
  Purchase #3 $54.75   11.764%   $61.1908   $61.19   $61.20   $61.20  
  Purchase #4 $49.71   4.731%   $52.0618   $52.06   $52.05   $52.10  
  Purchase #5 $152.49   6.529%   $162.4461   $162.45   $162.45   $162.40  
  Purchase #6 $189.31   11.428%   $210.9443   $210.94   $210.95   $210.90  
  Purchase #7 $18.48   3.119%   $19.0564   $19.06   $19.05   $19.10  
  7 purchase totals = $844.06       $930.9743   $930.98   $930.95   $931.00