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 $62.66   12.193%   $70.3001   $70.30   $70.30   $70.30  
  Purchase #2 $70.71   5.869%   $74.86   $74.86   $74.85   $74.90  
  Purchase #3 $40.95   11.197%   $45.5352   $45.54   $45.55   $45.50  
  Purchase #4 $40.35   3.283%   $41.6747   $41.67   $41.65   $41.70  
  Purchase #5 $245.44   4.794%   $257.2064   $257.21   $257.20   $257.20  
  Purchase #6 $170.55   8.806%   $185.5686   $185.57   $185.55   $185.60  
  Purchase #7 $77.32   3.817%   $80.2713   $80.27   $80.25   $80.30  
  7 purchase totals = $707.98       $755.4163   $755.42   $755.35   $755.50