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 $56.61   13.321%   $64.151   $64.15   $64.15   $64.20  
  Purchase #2 $109.64   13.197%   $124.1092   $124.11   $124.10   $124.10  
  Purchase #3 $194.55   9.450%   $212.935   $212.94   $212.95   $212.90  
  Purchase #4 $92.49   5.660%   $97.7249   $97.72   $97.70   $97.70  
  Purchase #5 $147.74   11.313%   $164.4538   $164.45   $164.45   $164.50  
  Purchase #6 $137.94   5.855%   $146.0164   $146.02   $146.00   $146.00  
  Purchase #7 $204.98   5.365%   $215.9772   $215.98   $216.00   $216.00  
  7 purchase totals = $943.95       $1,025.3675   $1,025.37   $1,025.35   $1,025.40