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 $43.83   10.812%   $48.5689   $48.57   $48.55   $48.60  
  Purchase #2 $211.83   11.401%   $235.9807   $235.98   $236.00   $236.00  
  Purchase #3 $51.97   11.417%   $57.9034   $57.90   $57.90   $57.90  
  Purchase #4 $211.61   8.122%   $228.797   $228.80   $228.80   $228.80  
  Purchase #5 $197.67   4.325%   $206.2192   $206.22   $206.20   $206.20  
  Purchase #6 $50.65   6.518%   $53.9514   $53.95   $53.95   $54.00  
  Purchase #7 $29.54   5.727%   $31.2318   $31.23   $31.25   $31.20  
  7 purchase totals = $797.10       $862.6524   $862.65   $862.65   $862.70