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 $86.74   10.541%   $95.8833   $95.88   $95.90   $95.90  
  Purchase #2 $115.84   11.416%   $129.0643   $129.06   $129.05   $129.10  
  Purchase #3 $188.79   8.431%   $204.7069   $204.71   $204.70   $204.70  
  Purchase #4 $75.97   9.360%   $83.0808   $83.08   $83.10   $83.10  
  Purchase #5 $14.63   6.812%   $15.6266   $15.63   $15.65   $15.60  
  Purchase #6 $203.49   3.828%   $211.2796   $211.28   $211.30   $211.30  
  Purchase #7 $79.69   6.676%   $85.0101   $85.01   $85.00   $85.00  
  7 purchase totals = $765.15       $824.6516   $824.65   $824.70   $824.70