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 $211.56   11.174%   $235.1997   $235.20   $235.20   $235.20  
  Purchase #2 $36.26   9.105%   $39.5615   $39.56   $39.55   $39.60  
  Purchase #3 $228.49   10.740%   $253.0298   $253.03   $253.05   $253.00  
  Purchase #4 $209.85   3.578%   $217.3584   $217.36   $217.35   $217.40  
  Purchase #5 $219.58   9.326%   $240.058   $240.06   $240.05   $240.10  
  Purchase #6 $54.76   9.307%   $59.8565   $59.86   $59.85   $59.90  
  Purchase #7 $67.37   4.476%   $70.3855   $70.39   $70.40   $70.40  
  7 purchase totals = $1,027.87       $1,115.4494   $1,115.46   $1,115.45   $1,115.60