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 $243.97   4.108%   $253.9923   $253.99   $254.00   $254.00  
  Purchase #2 $92.47   10.790%   $102.4475   $102.45   $102.45   $102.40  
  Purchase #3 $65.89   9.375%   $72.0672   $72.07   $72.05   $72.10  
  Purchase #4 $211.29   8.753%   $229.7842   $229.78   $229.80   $229.80  
  Purchase #5 $239.28   4.348%   $249.6839   $249.68   $249.70   $249.70  
  Purchase #6 $64.46   3.775%   $66.8934   $66.89   $66.90   $66.90  
  Purchase #7 $48.27   13.253%   $54.6672   $54.67   $54.65   $54.70  
  7 purchase totals = $965.63       $1,029.5357   $1,029.53   $1,029.55   $1,029.60