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 $200.27   13.813%   $227.9333   $227.93   $227.95   $227.90  
  Purchase #2 $115.68   12.230%   $129.8277   $129.83   $129.85   $129.80  
  Purchase #3 $49.53   12.210%   $55.5776   $55.58   $55.60   $55.60  
  Purchase #4 $244.74   9.829%   $268.7955   $268.80   $268.80   $268.80  
  Purchase #5 $234.33   13.638%   $266.2879   $266.29   $266.30   $266.30  
  Purchase #6 $212.48   13.276%   $240.6888   $240.69   $240.70   $240.70  
  Purchase #7 $8.38   11.781%   $9.3672   $9.37   $9.35   $9.40  
  7 purchase totals = $1,065.41       $1,198.4780   $1,198.49   $1,198.55   $1,198.50