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 $174.53   11.869%   $195.245   $195.25   $195.25   $195.20  
  Purchase #2 $42.86   5.472%   $45.2053   $45.21   $45.20   $45.20  
  Purchase #3 $160.55   3.715%   $166.5144   $166.51   $166.50   $166.50  
  Purchase #4 $169.99   12.474%   $191.1946   $191.19   $191.20   $191.20  
  Purchase #5 $11.70   7.831%   $12.6162   $12.62   $12.60   $12.60  
  Purchase #6 $87.52   8.460%   $94.9242   $94.92   $94.90   $94.90  
  Purchase #7 $240.41   4.298%   $250.7428   $250.74   $250.75   $250.70  
  7 purchase totals = $887.56       $956.4425   $956.44   $956.40   $956.30