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 $244.82   6.601%   $260.9806   $260.98   $261.00   $261.00  
  Purchase #2 $216.55   4.464%   $226.2168   $226.22   $226.20   $226.20  
  Purchase #3 $211.70   12.435%   $238.0249   $238.02   $238.00   $238.00  
  Purchase #4 $244.32   11.849%   $273.2695   $273.27   $273.25   $273.30  
  Purchase #5 $220.36   12.392%   $247.667   $247.67   $247.65   $247.70  
  Purchase #6 $171.87   10.536%   $189.9782   $189.98   $190.00   $190.00  
  Purchase #7 $28.65   8.155%   $30.9864   $30.99   $31.00   $31.00  
  7 purchase totals = $1,338.27       $1,467.1234   $1,467.13   $1,467.10   $1,467.20