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 $193.96   9.841%   $213.0476   $213.05   $213.05   $213.00  
  Purchase #2 $24.69   6.195%   $26.2195   $26.22   $26.20   $26.20  
  Purchase #3 $55.44   4.226%   $57.7829   $57.78   $57.80   $57.80  
  Purchase #4 $104.51   11.560%   $116.5914   $116.59   $116.60   $116.60  
  Purchase #5 $226.84   3.788%   $235.4327   $235.43   $235.45   $235.40  
  Purchase #6 $126.97   12.222%   $142.4883   $142.49   $142.50   $142.50  
  Purchase #7 $11.58   5.457%   $12.2119   $12.21   $12.20   $12.20  
  7 purchase totals = $743.99       $803.7743   $803.77   $803.80   $803.70