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 $60.91   12.737%   $68.6681   $68.67   $68.65   $68.70  
  Purchase #2 $167.78   8.164%   $181.4776   $181.48   $181.50   $181.50  
  Purchase #3 $213.99   9.166%   $233.6043   $233.60   $233.60   $233.60  
  Purchase #4 $203.98   4.196%   $212.539   $212.54   $212.55   $212.50  
  Purchase #5 $12.25   7.775%   $13.2024   $13.20   $13.20   $13.20  
  Purchase #6 $233.30   10.816%   $258.5337   $258.53   $258.55   $258.50  
  Purchase #7 $6.73   6.863%   $7.1919   $7.19   $7.20   $7.20  
  7 purchase totals = $898.94       $975.2170   $975.21   $975.25   $975.20