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 $68.73   11.160%   $76.4003   $76.40   $76.40   $76.40  
  Purchase #2 $223.96   5.200%   $235.6059   $235.61   $235.60   $235.60  
  Purchase #3 $103.62   13.639%   $117.7527   $117.75   $117.75   $117.80  
  Purchase #4 $212.38   3.180%   $219.1337   $219.13   $219.15   $219.10  
  Purchase #5 $84.38   10.419%   $93.1716   $93.17   $93.15   $93.20  
  Purchase #6 $147.62   3.535%   $152.8384   $152.84   $152.85   $152.80  
  Purchase #7 $139.68   11.603%   $155.8871   $155.89   $155.90   $155.90  
  7 purchase totals = $980.37       $1,050.7897   $1,050.79   $1,050.80   $1,050.80