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 $94.65   9.410%   $103.5566   $103.56   $103.55   $103.60  
  Purchase #2 $14.41   11.648%   $16.0885   $16.09   $16.10   $16.10  
  Purchase #3 $36.30   8.669%   $39.4468   $39.45   $39.45   $39.40  
  Purchase #4 $222.83   5.222%   $234.4662   $234.47   $234.45   $234.50  
  Purchase #5 $223.43   10.802%   $247.5649   $247.56   $247.55   $247.60  
  Purchase #6 $97.98   5.565%   $103.4326   $103.43   $103.45   $103.40  
  Purchase #7 $191.71   13.593%   $217.7691   $217.77   $217.75   $217.80  
  7 purchase totals = $881.31       $962.3247   $962.33   $962.30   $962.40