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 $31.98   6.872%   $34.1777   $34.18   $34.20   $34.20  
  Purchase #2 $213.33   6.527%   $227.254   $227.25   $227.25   $227.30  
  Purchase #3 $151.49   11.681%   $169.1855   $169.19   $169.20   $169.20  
  Purchase #4 $110.65   6.639%   $117.9961   $118.00   $118.00   $118.00  
  Purchase #5 $151.89   13.627%   $172.5881   $172.59   $172.60   $172.60  
  Purchase #6 $244.59   9.491%   $267.804   $267.80   $267.80   $267.80  
  Purchase #7 $157.42   8.845%   $171.3438   $171.34   $171.35   $171.30  
  7 purchase totals = $1,061.35       $1,160.3492   $1,160.35   $1,160.40   $1,160.40