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 $211.59   8.220%   $228.9827   $228.98   $229.00   $229.00  
  Purchase #2 $180.90   11.512%   $201.7252   $201.73   $201.75   $201.70  
  Purchase #3 $55.44   11.142%   $61.6171   $61.62   $61.60   $61.60  
  Purchase #4 $234.31   10.428%   $258.7438   $258.74   $258.75   $258.70  
  Purchase #5 $34.25   11.813%   $38.296   $38.30   $38.30   $38.30  
  Purchase #6 $213.71   5.220%   $224.8657   $224.87   $224.85   $224.90  
  Purchase #7 $183.61   10.109%   $202.1711   $202.17   $202.15   $202.20  
  7 purchase totals = $1,113.81       $1,216.4016   $1,216.41   $1,216.40   $1,216.40