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 $48.93   13.641%   $55.6045   $55.60   $55.60   $55.60  
  Purchase #2 $120.89   3.272%   $124.8455   $124.85   $124.85   $124.80  
  Purchase #3 $90.35   3.374%   $93.3984   $93.40   $93.40   $93.40  
  Purchase #4 $199.29   7.700%   $214.6353   $214.64   $214.65   $214.60  
  Purchase #5 $69.92   6.657%   $74.5746   $74.57   $74.55   $74.60  
  Purchase #6 $245.32   8.516%   $266.2115   $266.21   $266.20   $266.20  
  Purchase #7 $97.82   13.860%   $111.3779   $111.38   $111.40   $111.40  
  7 purchase totals = $872.52       $940.6477   $940.65   $940.65   $940.60