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 $67.52   5.376%   $71.1499   $71.15   $71.15   $71.10  
  Purchase #2 $211.84   9.740%   $232.4732   $232.47   $232.45   $232.50  
  Purchase #3 $34.80   13.230%   $39.404   $39.40   $39.40   $39.40  
  Purchase #4 $93.66   6.590%   $99.8322   $99.83   $99.85   $99.80  
  Purchase #5 $129.99   4.583%   $135.9474   $135.95   $135.95   $135.90  
  Purchase #6 $115.98   10.214%   $127.8262   $127.83   $127.85   $127.80  
  Purchase #7 $44.33   4.164%   $46.1759   $46.18   $46.20   $46.20  
  7 purchase totals = $698.12       $752.8088   $752.81   $752.85   $752.70