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 $62.80   4.432%   $65.5833   $65.58   $65.60   $65.60  
  Purchase #2 $235.59   7.247%   $252.6632   $252.66   $252.65   $252.70  
  Purchase #3 $19.73   4.781%   $20.6733   $20.67   $20.65   $20.70  
  Purchase #4 $67.93   6.331%   $72.2306   $72.23   $72.25   $72.20  
  Purchase #5 $7.47   3.780%   $7.7524   $7.75   $7.75   $7.80  
  Purchase #6 $145.94   11.688%   $162.9975   $163.00   $163.00   $163.00  
  Purchase #7 $45.78   7.536%   $49.23   $49.23   $49.25   $49.20  
  7 purchase totals = $585.24       $631.1303   $631.12   $631.15   $631.20