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 $63.69   4.824%   $66.7624   $66.76   $66.75   $66.80  
  Purchase #2 $198.39   9.372%   $216.9831   $216.98   $217.00   $217.00  
  Purchase #3 $57.55   6.707%   $61.4099   $61.41   $61.40   $61.40  
  Purchase #4 $224.34   7.377%   $240.8896   $240.89   $240.90   $240.90  
  Purchase #5 $213.94   9.153%   $233.5219   $233.52   $233.50   $233.50  
  Purchase #6 $121.72   6.627%   $129.7864   $129.79   $129.80   $129.80  
  Purchase #7 $82.48   13.760%   $93.8292   $93.83   $93.85   $93.80  
  7 purchase totals = $962.11       $1,043.1825   $1,043.18   $1,043.20   $1,043.20