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 $71.97   5.137%   $75.6671   $75.67   $75.65   $75.70  
  Purchase #2 $212.49   12.365%   $238.7644   $238.76   $238.75   $238.80  
  Purchase #3 $36.92   13.622%   $41.9492   $41.95   $41.95   $41.90  
  Purchase #4 $68.83   12.675%   $77.5542   $77.55   $77.55   $77.60  
  Purchase #5 $88.49   8.654%   $96.1479   $96.15   $96.15   $96.10  
  Purchase #6 $158.89   12.158%   $178.2078   $178.21   $178.20   $178.20  
  Purchase #7 $235.26   6.116%   $249.6485   $249.65   $249.65   $249.60  
  7 purchase totals = $872.85       $957.9391   $957.94   $957.90   $957.90