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 $86.61   12.655%   $97.5705   $97.57   $97.55   $97.60  
  Purchase #2 $134.48   6.626%   $143.3906   $143.39   $143.40   $143.40  
  Purchase #3 $137.36   11.537%   $153.2072   $153.21   $153.20   $153.20  
  Purchase #4 $81.44   6.607%   $86.8207   $86.82   $86.80   $86.80  
  Purchase #5 $240.42   11.551%   $268.1909   $268.19   $268.20   $268.20  
  Purchase #6 $159.60   8.391%   $172.992   $172.99   $173.00   $173.00  
  Purchase #7 $21.97   9.150%   $23.9803   $23.98   $24.00   $24.00  
  7 purchase totals = $861.88       $946.1522   $946.15   $946.15   $946.20