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 $127.64   9.704%   $140.0262   $140.03   $140.05   $140.00  
  Purchase #2 $133.27   12.717%   $150.2179   $150.22   $150.20   $150.20  
  Purchase #3 $43.42   9.710%   $47.6361   $47.64   $47.65   $47.60  
  Purchase #4 $6.68   5.198%   $7.0272   $7.03   $7.05   $7.00  
  Purchase #5 $150.37   12.830%   $169.6625   $169.66   $169.65   $169.70  
  Purchase #6 $55.34   7.488%   $59.4839   $59.48   $59.50   $59.50  
  Purchase #7 $86.62   8.546%   $94.0225   $94.02   $94.00   $94.00  
  7 purchase totals = $603.34       $668.0763   $668.08   $668.10   $668.00