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 $113.39   11.792%   $126.7609   $126.76   $126.75   $126.80  
  Purchase #2 $39.58   5.342%   $41.6944   $41.69   $41.70   $41.70  
  Purchase #3 $86.77   13.515%   $98.497   $98.50   $98.50   $98.50  
  Purchase #4 $247.50   4.666%   $259.0484   $259.05   $259.05   $259.00  
  Purchase #5 $9.48   13.738%   $10.7824   $10.78   $10.80   $10.80  
  Purchase #6 $230.45   11.654%   $257.3066   $257.31   $257.30   $257.30  
  Purchase #7 $221.52   6.529%   $235.983   $235.98   $236.00   $236.00  
  7 purchase totals = $948.69       $1,030.0727   $1,030.07   $1,030.10   $1,030.10