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 $247.86   11.650%   $276.7357   $276.74   $276.75   $276.70  
  Purchase #2 $222.84   12.788%   $251.3368   $251.34   $251.35   $251.30  
  Purchase #3 $92.89   11.441%   $103.5175   $103.52   $103.50   $103.50  
  Purchase #4 $224.82   4.855%   $235.735   $235.74   $235.75   $235.70  
  Purchase #5 $165.61   9.455%   $181.2684   $181.27   $181.25   $181.30  
  Purchase #6 $155.77   11.385%   $173.5044   $173.50   $173.50   $173.50  
  Purchase #7 $98.50   3.498%   $101.9455   $101.95   $101.95   $101.90  
  7 purchase totals = $1,208.29       $1,324.0433   $1,324.06   $1,324.05   $1,323.90