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 $105.98   13.803%   $120.6084   $120.61   $120.60   $120.60  
  Purchase #2 $237.63   6.772%   $253.7223   $253.72   $253.70   $253.70  
  Purchase #3 $168.82   4.258%   $176.0084   $176.01   $176.00   $176.00  
  Purchase #4 $247.33   11.184%   $274.9914   $274.99   $275.00   $275.00  
  Purchase #5 $8.95   10.117%   $9.8555   $9.86   $9.85   $9.90  
  Purchase #6 $59.38   3.596%   $61.5153   $61.52   $61.50   $61.50  
  Purchase #7 $230.82   11.381%   $257.0896   $257.09   $257.10   $257.10  
  7 purchase totals = $1,058.91       $1,153.7909   $1,153.80   $1,153.75   $1,153.80