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 $72.25   7.292%   $77.5185   $77.52   $77.50   $77.50  
  Purchase #2 $110.96   13.758%   $126.2259   $126.23   $126.25   $126.20  
  Purchase #3 $243.27   13.445%   $275.9777   $275.98   $276.00   $276.00  
  Purchase #4 $204.29   11.197%   $227.1644   $227.16   $227.15   $227.20  
  Purchase #5 $143.57   13.795%   $163.3755   $163.38   $163.40   $163.40  
  Purchase #6 $61.50   4.796%   $64.4495   $64.45   $64.45   $64.40  
  Purchase #7 $243.88   6.198%   $258.9957   $259.00   $259.00   $259.00  
  7 purchase totals = $1,079.72       $1,193.7072   $1,193.72   $1,193.75   $1,193.70