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 $116.31   7.138%   $124.6122   $124.61   $124.60   $124.60  
  Purchase #2 $134.54   4.707%   $140.8728   $140.87   $140.85   $140.90  
  Purchase #3 $227.49   13.739%   $258.7449   $258.74   $258.75   $258.70  
  Purchase #4 $87.56   8.826%   $95.288   $95.29   $95.30   $95.30  
  Purchase #5 $64.75   6.711%   $69.0954   $69.10   $69.10   $69.10  
  Purchase #6 $8.52   9.623%   $9.3399   $9.34   $9.35   $9.30  
  Purchase #7 $158.94   6.120%   $168.6671   $168.67   $168.65   $168.70  
  7 purchase totals = $798.11       $866.6203   $866.62   $866.60   $866.60