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 $203.98   6.844%   $217.9404   $217.94   $217.95   $217.90  
  Purchase #2 $44.94   10.809%   $49.7976   $49.80   $49.80   $49.80  
  Purchase #3 $18.60   5.113%   $19.551   $19.55   $19.55   $19.60  
  Purchase #4 $235.82   9.607%   $258.4752   $258.48   $258.50   $258.50  
  Purchase #5 $190.78   11.665%   $213.0345   $213.03   $213.05   $213.00  
  Purchase #6 $172.95   11.607%   $193.0243   $193.02   $193.00   $193.00  
  Purchase #7 $6.89   13.231%   $7.8016   $7.80   $7.80   $7.80  
  7 purchase totals = $873.96       $959.6246   $959.62   $959.65   $959.60