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 $79.63   11.477%   $88.7691   $88.77   $88.75   $88.80  
  Purchase #2 $112.44   12.632%   $126.6434   $126.64   $126.65   $126.60  
  Purchase #3 $241.60   5.861%   $255.7602   $255.76   $255.75   $255.80  
  Purchase #4 $49.55   13.865%   $56.4201   $56.42   $56.40   $56.40  
  Purchase #5 $59.76   7.594%   $64.2982   $64.30   $64.30   $64.30  
  Purchase #6 $207.66   5.760%   $219.6212   $219.62   $219.60   $219.60  
  Purchase #7 $197.93   7.107%   $211.9969   $212.00   $212.00   $212.00  
  7 purchase totals = $948.57       $1,023.5091   $1,023.51   $1,023.45   $1,023.50