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 $71.51   6.757%   $76.3419   $76.34   $76.35   $76.30  
  Purchase #2 $127.26   6.496%   $135.5268   $135.53   $135.55   $135.50  
  Purchase #3 $144.42   8.256%   $156.3433   $156.34   $156.35   $156.30  
  Purchase #4 $51.28   11.618%   $57.2377   $57.24   $57.25   $57.20  
  Purchase #5 $145.80   4.464%   $152.3085   $152.31   $152.30   $152.30  
  Purchase #6 $5.48   10.188%   $6.0383   $6.04   $6.05   $6.00  
  Purchase #7 $231.82   8.529%   $251.5919   $251.59   $251.60   $251.60  
  7 purchase totals = $777.57       $835.3884   $835.39   $835.45   $835.20