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 $239.65   5.624%   $253.1279   $253.13   $253.15   $253.10  
  Purchase #2 $58.82   11.131%   $65.3673   $65.37   $65.35   $65.40  
  Purchase #3 $118.89   7.454%   $127.7521   $127.75   $127.75   $127.80  
  Purchase #4 $188.98   4.749%   $197.9547   $197.95   $197.95   $198.00  
  Purchase #5 $206.81   8.582%   $224.5584   $224.56   $224.55   $224.60  
  Purchase #6 $191.81   6.251%   $203.8   $203.80   $203.80   $203.80  
  Purchase #7 $111.68   11.698%   $124.7443   $124.74   $124.75   $124.70  
  7 purchase totals = $1,116.64       $1,197.3047   $1,197.30   $1,197.30   $1,197.40