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 $239.95   10.566%   $265.3031   $265.30   $265.30   $265.30  
  Purchase #2 $119.32   3.279%   $123.2325   $123.23   $123.25   $123.20  
  Purchase #3 $111.36   13.426%   $126.3112   $126.31   $126.30   $126.30  
  Purchase #4 $151.67   11.865%   $169.6656   $169.67   $169.65   $169.70  
  Purchase #5 $72.53   3.574%   $75.1222   $75.12   $75.10   $75.10  
  Purchase #6 $27.65   6.775%   $29.5233   $29.52   $29.50   $29.50  
  Purchase #7 $194.95   11.846%   $218.0438   $218.04   $218.05   $218.00  
  7 purchase totals = $917.43       $1,007.2017   $1,007.19   $1,007.15   $1,007.10