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 $156.59   11.778%   $175.0332   $175.03   $175.05   $175.00  
  Purchase #2 $209.64   4.455%   $218.9795   $218.98   $219.00   $219.00  
  Purchase #3 $246.48   8.757%   $268.0643   $268.06   $268.05   $268.10  
  Purchase #4 $151.51   11.426%   $168.8215   $168.82   $168.80   $168.80  
  Purchase #5 $58.65   10.589%   $64.8604   $64.86   $64.85   $64.90  
  Purchase #6 $34.74   4.589%   $36.3342   $36.33   $36.35   $36.30  
  Purchase #7 $18.41   4.614%   $19.2594   $19.26   $19.25   $19.30  
  7 purchase totals = $876.02       $951.3525   $951.34   $951.35   $951.40