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 $66.92   12.112%   $75.0254   $75.03   $75.05   $75.00  
  Purchase #2 $66.67   6.418%   $70.9489   $70.95   $70.95   $70.90  
  Purchase #3 $113.90   4.731%   $119.2886   $119.29   $119.30   $119.30  
  Purchase #4 $195.99   4.643%   $205.0898   $205.09   $205.10   $205.10  
  Purchase #5 $66.89   3.121%   $68.9776   $68.98   $69.00   $69.00  
  Purchase #6 $132.72   4.287%   $138.4097   $138.41   $138.40   $138.40  
  Purchase #7 $113.80   10.436%   $125.6762   $125.68   $125.70   $125.70  
  7 purchase totals = $756.89       $803.4162   $803.43   $803.50   $803.40