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 $74.33   13.477%   $84.3475   $84.35   $84.35   $84.30  
  Purchase #2 $55.49   11.622%   $61.939   $61.94   $61.95   $61.90  
  Purchase #3 $12.66   5.864%   $13.4024   $13.40   $13.40   $13.40  
  Purchase #4 $196.54   6.778%   $209.8615   $209.86   $209.85   $209.90  
  Purchase #5 $219.98   11.146%   $244.499   $244.50   $244.50   $244.50  
  Purchase #6 $99.88   3.792%   $103.6674   $103.67   $103.65   $103.70  
  Purchase #7 $194.64   5.865%   $206.0556   $206.06   $206.05   $206.10  
  7 purchase totals = $853.52       $923.7724   $923.78   $923.75   $923.80