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 $193.71   11.224%   $215.452   $215.45   $215.45   $215.50  
  Purchase #2 $62.57   8.479%   $67.8753   $67.88   $67.90   $67.90  
  Purchase #3 $25.61   13.665%   $29.1096   $29.11   $29.10   $29.10  
  Purchase #4 $96.93   13.822%   $110.3277   $110.33   $110.35   $110.30  
  Purchase #5 $64.61   9.517%   $70.7589   $70.76   $70.75   $70.80  
  Purchase #6 $53.67   11.843%   $60.0261   $60.03   $60.05   $60.00  
  Purchase #7 $9.76   13.297%   $11.0578   $11.06   $11.05   $11.10  
  7 purchase totals = $506.86       $564.6074   $564.62   $564.65   $564.70