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 $159.78   9.874%   $175.5567   $175.56   $175.55   $175.60  
  Purchase #2 $239.32   5.226%   $251.8269   $251.83   $251.85   $251.80  
  Purchase #3 $244.85   11.447%   $272.878   $272.88   $272.90   $272.90  
  Purchase #4 $76.99   8.416%   $83.4695   $83.47   $83.45   $83.50  
  Purchase #5 $207.31   10.391%   $228.8516   $228.85   $228.85   $228.90  
  Purchase #6 $134.78   8.741%   $146.5611   $146.56   $146.55   $146.60  
  Purchase #7 $16.31   3.274%   $16.844   $16.84   $16.85   $16.80  
  7 purchase totals = $1,079.34       $1,175.9878   $1,175.99   $1,176.00   $1,176.10