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 $250.47   10.666%   $277.1851   $277.19   $277.20   $277.20  
  Purchase #2 $61.92   12.583%   $69.7114   $69.71   $69.70   $69.70  
  Purchase #3 $26.47   3.679%   $27.4438   $27.44   $27.45   $27.40  
  Purchase #4 $93.49   9.315%   $102.1986   $102.20   $102.20   $102.20  
  Purchase #5 $167.55   7.639%   $180.3491   $180.35   $180.35   $180.30  
  Purchase #6 $36.78   11.414%   $40.9781   $40.98   $41.00   $41.00  
  Purchase #7 $54.68   3.170%   $56.4134   $56.41   $56.40   $56.40  
  7 purchase totals = $691.36       $754.2795   $754.28   $754.30   $754.20