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 $158.31   6.756%   $169.0054   $169.01   $169.00   $169.00  
  Purchase #2 $202.31   12.620%   $227.8415   $227.84   $227.85   $227.80  
  Purchase #3 $12.53   6.583%   $13.3548   $13.35   $13.35   $13.40  
  Purchase #4 $170.40   3.825%   $176.9178   $176.92   $176.90   $176.90  
  Purchase #5 $178.95   8.138%   $193.513   $193.51   $193.50   $193.50  
  Purchase #6 $47.52   7.803%   $51.228   $51.23   $51.25   $51.20  
  Purchase #7 $182.77   11.757%   $204.2583   $204.26   $204.25   $204.30  
  7 purchase totals = $952.79       $1,036.1188   $1,036.12   $1,036.10   $1,036.10