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 $60.83   8.169%   $65.7992   $65.80   $65.80   $65.80  
  Purchase #2 $121.28   4.535%   $126.78   $126.78   $126.80   $126.80  
  Purchase #3 $33.77   11.834%   $37.7663   $37.77   $37.75   $37.80  
  Purchase #4 $246.97   4.236%   $257.4316   $257.43   $257.45   $257.40  
  Purchase #5 $45.45   6.318%   $48.3215   $48.32   $48.30   $48.30  
  Purchase #6 $24.71   9.445%   $27.0439   $27.04   $27.05   $27.00  
  Purchase #7 $174.81   10.628%   $193.3888   $193.39   $193.40   $193.40  
  7 purchase totals = $707.82       $756.5313   $756.53   $756.55   $756.50