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 $61.73   7.722%   $66.4968   $66.50   $66.50   $66.50  
  Purchase #2 $206.56   6.333%   $219.6414   $219.64   $219.65   $219.60  
  Purchase #3 $143.40   12.578%   $161.4369   $161.44   $161.45   $161.40  
  Purchase #4 $189.68   10.207%   $209.0406   $209.04   $209.05   $209.00  
  Purchase #5 $176.91   8.115%   $191.2662   $191.27   $191.25   $191.30  
  Purchase #6 $36.36   12.357%   $40.853   $40.85   $40.85   $40.90  
  Purchase #7 $155.62   3.736%   $161.434   $161.43   $161.45   $161.40  
  7 purchase totals = $970.26       $1,050.1689   $1,050.17   $1,050.20   $1,050.10