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 $91.58   7.371%   $98.3304   $98.33   $98.35   $98.30  
  Purchase #2 $57.67   9.518%   $63.159   $63.16   $63.15   $63.20  
  Purchase #3 $64.34   6.532%   $68.5427   $68.54   $68.55   $68.50  
  Purchase #4 $240.34   7.755%   $258.9784   $258.98   $259.00   $259.00  
  Purchase #5 $55.71   3.700%   $57.7713   $57.77   $57.75   $57.80  
  Purchase #6 $233.83   11.393%   $260.4703   $260.47   $260.45   $260.50  
  Purchase #7 $122.59   10.787%   $135.8138   $135.81   $135.80   $135.80  
  7 purchase totals = $866.06       $943.0659   $943.06   $943.05   $943.10