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 $201.55   12.468%   $226.6793   $226.68   $226.70   $226.70  
  Purchase #2 $100.25   9.259%   $109.5321   $109.53   $109.55   $109.50  
  Purchase #3 $52.61   3.493%   $54.4477   $54.45   $54.45   $54.40  
  Purchase #4 $213.57   5.652%   $225.641   $225.64   $225.65   $225.60  
  Purchase #5 $212.31   5.843%   $224.7153   $224.72   $224.70   $224.70  
  Purchase #6 $170.52   7.177%   $182.7582   $182.76   $182.75   $182.80  
  Purchase #7 $19.71   5.408%   $20.7759   $20.78   $20.80   $20.80  
  7 purchase totals = $970.52       $1,044.5495   $1,044.56   $1,044.60   $1,044.50