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 $217.80   9.254%   $237.9552   $237.96   $237.95   $238.00  
  Purchase #2 $159.38   7.506%   $171.3431   $171.34   $171.35   $171.30  
  Purchase #3 $242.43   3.286%   $250.3962   $250.40   $250.40   $250.40  
  Purchase #4 $170.48   4.654%   $178.4141   $178.41   $178.40   $178.40  
  Purchase #5 $108.28   4.457%   $113.106   $113.11   $113.10   $113.10  
  Purchase #6 $61.91   6.111%   $65.6933   $65.69   $65.70   $65.70  
  Purchase #7 $151.43   3.862%   $157.2782   $157.28   $157.30   $157.30  
  7 purchase totals = $1,111.71       $1,174.1861   $1,174.19   $1,174.20   $1,174.20