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 $58.28   3.511%   $60.3262   $60.33   $60.35   $60.30  
  Purchase #2 $88.40   5.153%   $92.9553   $92.96   $92.95   $93.00  
  Purchase #3 $33.93   11.270%   $37.7539   $37.75   $37.75   $37.80  
  Purchase #4 $95.81   9.261%   $104.683   $104.68   $104.70   $104.70  
  Purchase #5 $160.75   9.395%   $175.8525   $175.85   $175.85   $175.90  
  Purchase #6 $114.65   6.770%   $122.4118   $122.41   $122.40   $122.40  
  Purchase #7 $146.76   9.825%   $161.1792   $161.18   $161.20   $161.20  
  7 purchase totals = $698.58       $755.1619   $755.16   $755.20   $755.30