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 $14.66   11.319%   $16.3194   $16.32   $16.30   $16.30  
  Purchase #2 $195.34   5.424%   $205.9352   $205.94   $205.95   $205.90  
  Purchase #3 $26.35   10.648%   $29.1557   $29.16   $29.15   $29.20  
  Purchase #4 $69.52   10.857%   $77.0678   $77.07   $77.05   $77.10  
  Purchase #5 $104.29   8.205%   $112.847   $112.85   $112.85   $112.80  
  Purchase #6 $235.78   4.730%   $246.9324   $246.93   $246.95   $246.90  
  Purchase #7 $63.30   10.114%   $69.7022   $69.70   $69.70   $69.70  
  7 purchase totals = $709.24       $757.9597   $757.97   $757.95   $757.90