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 $245.59   7.521%   $264.0608   $264.06   $264.05   $264.10  
  Purchase #2 $124.76   12.742%   $140.6569   $140.66   $140.65   $140.70  
  Purchase #3 $226.53   8.304%   $245.3411   $245.34   $245.35   $245.30  
  Purchase #4 $200.99   5.490%   $212.0244   $212.02   $212.00   $212.00  
  Purchase #5 $85.29   7.731%   $91.8838   $91.88   $91.90   $91.90  
  Purchase #6 $6.69   7.467%   $7.1895   $7.19   $7.20   $7.20  
  Purchase #7 $117.97   7.505%   $126.8236   $126.82   $126.80   $126.80  
  7 purchase totals = $1,007.82       $1,087.9801   $1,087.97   $1,087.95   $1,088.00