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 $193.49   5.612%   $204.3487   $204.35   $204.35   $204.30  
  Purchase #2 $162.96   6.501%   $173.554   $173.55   $173.55   $173.60  
  Purchase #3 $174.87   12.317%   $196.4087   $196.41   $196.40   $196.40  
  Purchase #4 $180.80   5.780%   $191.2502   $191.25   $191.25   $191.30  
  Purchase #5 $190.57   7.657%   $205.1619   $205.16   $205.15   $205.20  
  Purchase #6 $237.76   12.425%   $267.3017   $267.30   $267.30   $267.30  
  Purchase #7 $44.52   11.754%   $49.7529   $49.75   $49.75   $49.80  
  7 purchase totals = $1,184.97       $1,287.7781   $1,287.77   $1,287.75   $1,287.90