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 $133.59   11.614%   $149.1051   $149.11   $149.10   $149.10  
  Purchase #2 $201.82   11.391%   $224.8093   $224.81   $224.80   $224.80  
  Purchase #3 $58.65   9.771%   $64.3807   $64.38   $64.40   $64.40  
  Purchase #4 $171.60   3.849%   $178.2049   $178.20   $178.20   $178.20  
  Purchase #5 $25.26   5.230%   $26.5811   $26.58   $26.60   $26.60  
  Purchase #6 $244.99   11.852%   $274.0262   $274.03   $274.05   $274.00  
  Purchase #7 $229.86   4.573%   $240.3715   $240.37   $240.35   $240.40  
  7 purchase totals = $1,065.77       $1,157.4788   $1,157.48   $1,157.50   $1,157.50