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 $11.56   8.873%   $12.5857   $12.59   $12.60   $12.60  
  Purchase #2 $159.75   9.354%   $174.693   $174.69   $174.70   $174.70  
  Purchase #3 $62.30   9.462%   $68.1948   $68.19   $68.20   $68.20  
  Purchase #4 $194.69   4.278%   $203.0188   $203.02   $203.00   $203.00  
  Purchase #5 $173.53   10.341%   $191.4747   $191.47   $191.45   $191.50  
  Purchase #6 $6.34   4.199%   $6.6062   $6.61   $6.60   $6.60  
  Purchase #7 $245.57   5.156%   $258.2316   $258.23   $258.25   $258.20  
  7 purchase totals = $853.74       $914.8048   $914.80   $914.80   $914.80