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 $116.68   13.134%   $132.0048   $132.00   $132.00   $132.00  
  Purchase #2 $199.66   10.199%   $220.0233   $220.02   $220.00   $220.00  
  Purchase #3 $16.58   13.460%   $18.8117   $18.81   $18.80   $18.80  
  Purchase #4 $188.61   12.120%   $211.4695   $211.47   $211.45   $211.50  
  Purchase #5 $174.78   13.691%   $198.7091   $198.71   $198.70   $198.70  
  Purchase #6 $238.96   10.343%   $263.6756   $263.68   $263.70   $263.70  
  Purchase #7 $14.38   3.494%   $14.8824   $14.88   $14.90   $14.90  
  7 purchase totals = $949.65       $1,059.5764   $1,059.57   $1,059.55   $1,059.60