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 $58.71   8.174%   $63.509   $63.51   $63.50   $63.50  
  Purchase #2 $92.78   3.223%   $95.7703   $95.77   $95.75   $95.80  
  Purchase #3 $214.71   6.497%   $228.6597   $228.66   $228.65   $228.70  
  Purchase #4 $230.30   7.560%   $247.7107   $247.71   $247.70   $247.70  
  Purchase #5 $143.55   10.761%   $158.9974   $159.00   $159.00   $159.00  
  Purchase #6 $70.38   5.465%   $74.2263   $74.23   $74.25   $74.20  
  Purchase #7 $237.98   11.234%   $264.7147   $264.71   $264.70   $264.70  
  7 purchase totals = $1,048.41       $1,133.5881   $1,133.59   $1,133.55   $1,133.60