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 $207.64   9.409%   $227.1768   $227.18   $227.20   $227.20  
  Purchase #2 $87.74   9.322%   $95.9191   $95.92   $95.90   $95.90  
  Purchase #3 $159.33   8.871%   $173.4642   $173.46   $173.45   $173.50  
  Purchase #4 $176.42   13.499%   $200.2349   $200.23   $200.25   $200.20  
  Purchase #5 $210.97   11.292%   $234.7927   $234.79   $234.80   $234.80  
  Purchase #6 $203.59   3.816%   $211.359   $211.36   $211.35   $211.40  
  Purchase #7 $64.62   8.374%   $70.0313   $70.03   $70.05   $70.00  
  7 purchase totals = $1,110.31       $1,212.9780   $1,212.97   $1,213.00   $1,213.00