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 $204.46   9.616%   $224.1209   $224.12   $224.10   $224.10  
  Purchase #2 $56.47   8.613%   $61.3338   $61.33   $61.35   $61.30  
  Purchase #3 $188.71   8.431%   $204.6201   $204.62   $204.60   $204.60  
  Purchase #4 $245.63   13.568%   $278.9571   $278.96   $278.95   $279.00  
  Purchase #5 $172.61   11.814%   $193.0021   $193.00   $193.00   $193.00  
  Purchase #6 $171.62   8.226%   $185.7375   $185.74   $185.75   $185.70  
  Purchase #7 $57.28   8.859%   $62.3544   $62.35   $62.35   $62.40  
  7 purchase totals = $1,096.78       $1,210.1259   $1,210.12   $1,210.10   $1,210.10