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 $242.76   5.599%   $256.3521   $256.35   $256.35   $256.40  
  Purchase #2 $93.92   7.527%   $100.9894   $100.99   $101.00   $101.00  
  Purchase #3 $120.86   7.389%   $129.7903   $129.79   $129.80   $129.80  
  Purchase #4 $139.81   6.561%   $148.9829   $148.98   $149.00   $149.00  
  Purchase #5 $224.28   7.466%   $241.0247   $241.02   $241.00   $241.00  
  Purchase #6 $59.98   3.361%   $61.9959   $62.00   $62.00   $62.00  
  Purchase #7 $210.57   4.261%   $219.5424   $219.54   $219.55   $219.50  
  7 purchase totals = $1,092.18       $1,158.6777   $1,158.67   $1,158.70   $1,158.70