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 $67.86   8.811%   $73.8391   $73.84   $73.85   $73.80  
  Purchase #2 $94.67   4.739%   $99.1564   $99.16   $99.15   $99.20  
  Purchase #3 $11.50   5.471%   $12.1292   $12.13   $12.15   $12.10  
  Purchase #4 $109.52   12.497%   $123.2067   $123.21   $123.20   $123.20  
  Purchase #5 $161.35   6.383%   $171.649   $171.65   $171.65   $171.60  
  Purchase #6 $53.69   12.539%   $60.4222   $60.42   $60.40   $60.40  
  Purchase #7 $232.99   9.856%   $255.9535   $255.95   $255.95   $256.00  
  7 purchase totals = $731.58       $796.3561   $796.36   $796.35   $796.30