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 $246.29   10.432%   $271.983   $271.98   $272.00   $272.00  
  Purchase #2 $214.29   10.608%   $237.0219   $237.02   $237.00   $237.00  
  Purchase #3 $45.65   6.278%   $48.5159   $48.52   $48.50   $48.50  
  Purchase #4 $111.44   6.191%   $118.3393   $118.34   $118.35   $118.30  
  Purchase #5 $243.25   9.527%   $266.4244   $266.42   $266.40   $266.40  
  Purchase #6 $51.46   13.446%   $58.3793   $58.38   $58.40   $58.40  
  Purchase #7 $216.29   4.253%   $225.4888   $225.49   $225.50   $225.50  
  7 purchase totals = $1,128.67       $1,226.1526   $1,226.15   $1,226.15   $1,226.10