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 $76.73   10.555%   $84.8289   $84.83   $84.85   $84.80  
  Purchase #2 $127.52   6.395%   $135.6749   $135.67   $135.65   $135.70  
  Purchase #3 $14.36   11.553%   $16.019   $16.02   $16.00   $16.00  
  Purchase #4 $136.35   4.176%   $142.044   $142.04   $142.05   $142.00  
  Purchase #5 $51.85   4.705%   $54.2895   $54.29   $54.30   $54.30  
  Purchase #6 $200.61   10.552%   $221.7784   $221.78   $221.80   $221.80  
  Purchase #7 $118.63   12.709%   $133.7067   $133.71   $133.70   $133.70  
  7 purchase totals = $726.05       $788.3414   $788.34   $788.35   $788.30