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 $197.29   12.535%   $222.0203   $222.02   $222.00   $222.00  
  Purchase #2 $217.84   4.438%   $227.5077   $227.51   $227.50   $227.50  
  Purchase #3 $195.36   7.306%   $209.633   $209.63   $209.65   $209.60  
  Purchase #4 $140.63   11.568%   $156.8981   $156.90   $156.90   $156.90  
  Purchase #5 $147.27   9.321%   $160.997   $161.00   $161.00   $161.00  
  Purchase #6 $59.54   12.319%   $66.8747   $66.87   $66.85   $66.90  
  Purchase #7 $23.68   3.779%   $24.5749   $24.57   $24.55   $24.60  
  7 purchase totals = $981.61       $1,068.5057   $1,068.50   $1,068.45   $1,068.50