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 $47.86   11.202%   $53.2213   $53.22   $53.20   $53.20  
  Purchase #2 $101.56   7.826%   $109.5081   $109.51   $109.50   $109.50  
  Purchase #3 $213.69   5.201%   $224.804   $224.80   $224.80   $224.80  
  Purchase #4 $106.26   4.104%   $110.6209   $110.62   $110.60   $110.60  
  Purchase #5 $243.33   7.154%   $260.7378   $260.74   $260.75   $260.70  
  Purchase #6 $83.79   4.152%   $87.269   $87.27   $87.25   $87.30  
  Purchase #7 $211.51   8.649%   $229.8035   $229.80   $229.80   $229.80  
  7 purchase totals = $1,008.00       $1,075.9646   $1,075.96   $1,075.90   $1,075.90