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 $98.67   11.547%   $110.0634   $110.06   $110.05   $110.10  
  Purchase #2 $125.38   9.700%   $137.5419   $137.54   $137.55   $137.50  
  Purchase #3 $113.29   5.841%   $119.9073   $119.91   $119.90   $119.90  
  Purchase #4 $44.45   3.808%   $46.1427   $46.14   $46.15   $46.10  
  Purchase #5 $22.74   11.580%   $25.3733   $25.37   $25.35   $25.40  
  Purchase #6 $246.98   10.398%   $272.661   $272.66   $272.65   $272.70  
  Purchase #7 $228.64   5.115%   $240.3349   $240.33   $240.35   $240.30  
  7 purchase totals = $880.15       $952.0245   $952.01   $952.00   $952.00