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 $40.98   7.272%   $43.9601   $43.96   $43.95   $44.00  
  Purchase #2 $245.95   4.807%   $257.7728   $257.77   $257.75   $257.80  
  Purchase #3 $234.27   11.151%   $260.3934   $260.39   $260.40   $260.40  
  Purchase #4 $212.83   3.232%   $219.7087   $219.71   $219.70   $219.70  
  Purchase #5 $155.90   6.390%   $165.862   $165.86   $165.85   $165.90  
  Purchase #6 $38.92   5.623%   $41.1085   $41.11   $41.10   $41.10  
  Purchase #7 $204.94   5.123%   $215.4391   $215.44   $215.45   $215.40  
  7 purchase totals = $1,133.79       $1,204.2446   $1,204.24   $1,204.20   $1,204.30