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 $57.75   4.790%   $60.5162   $60.52   $60.50   $60.50  
  Purchase #2 $112.86   10.257%   $124.4361   $124.44   $124.45   $124.40  
  Purchase #3 $25.42   6.681%   $27.1183   $27.12   $27.10   $27.10  
  Purchase #4 $93.83   11.479%   $104.6007   $104.60   $104.60   $104.60  
  Purchase #5 $172.87   6.683%   $184.4229   $184.42   $184.40   $184.40  
  Purchase #6 $168.91   8.787%   $183.7521   $183.75   $183.75   $183.80  
  Purchase #7 $122.58   3.270%   $126.5884   $126.59   $126.60   $126.60  
  7 purchase totals = $754.22       $811.4347   $811.44   $811.40   $811.40