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 $74.40   3.769%   $77.2041   $77.20   $77.20   $77.20  
  Purchase #2 $189.64   9.858%   $208.3347   $208.33   $208.35   $208.30  
  Purchase #3 $117.39   4.781%   $123.0024   $123.00   $123.00   $123.00  
  Purchase #4 $101.95   11.687%   $113.8649   $113.86   $113.85   $113.90  
  Purchase #5 $185.95   12.783%   $209.72   $209.72   $209.70   $209.70  
  Purchase #6 $187.54   9.291%   $204.9643   $204.96   $204.95   $205.00  
  Purchase #7 $58.99   8.844%   $64.2071   $64.21   $64.20   $64.20  
  7 purchase totals = $915.86       $1,001.2975   $1,001.28   $1,001.25   $1,001.30