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 $164.96   5.334%   $173.759   $173.76   $173.75   $173.80  
  Purchase #2 $116.68   4.502%   $121.9329   $121.93   $121.95   $121.90  
  Purchase #3 $75.81   8.277%   $82.0848   $82.08   $82.10   $82.10  
  Purchase #4 $247.85   6.827%   $264.7707   $264.77   $264.75   $264.80  
  Purchase #5 $118.42   9.685%   $129.889   $129.89   $129.90   $129.90  
  Purchase #6 $243.69   9.840%   $267.6691   $267.67   $267.65   $267.70  
  Purchase #7 $222.53   10.563%   $246.0358   $246.04   $246.05   $246.00  
  7 purchase totals = $1,189.94       $1,286.1413   $1,286.14   $1,286.15   $1,286.20