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 $86.63   7.108%   $92.7877   $92.79   $92.80   $92.80  
  Purchase #2 $23.65   6.827%   $25.2646   $25.26   $25.25   $25.30  
  Purchase #3 $48.95   9.266%   $53.4857   $53.49   $53.50   $53.50  
  Purchase #4 $237.89   3.568%   $246.3779   $246.38   $246.40   $246.40  
  Purchase #5 $226.68   13.586%   $257.4767   $257.48   $257.50   $257.50  
  Purchase #6 $171.84   5.453%   $181.2104   $181.21   $181.20   $181.20  
  Purchase #7 $93.48   12.861%   $105.5025   $105.50   $105.50   $105.50  
  7 purchase totals = $889.12       $962.1055   $962.11   $962.15   $962.20