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 $95.81   5.218%   $100.8094   $100.81   $100.80   $100.80  
  Purchase #2 $154.70   12.716%   $174.3717   $174.37   $174.35   $174.40  
  Purchase #3 $16.54   11.747%   $18.483   $18.48   $18.50   $18.50  
  Purchase #4 $59.98   8.210%   $64.9044   $64.90   $64.90   $64.90  
  Purchase #5 $193.68   8.135%   $209.4359   $209.44   $209.45   $209.40  
  Purchase #6 $155.94   12.133%   $174.8602   $174.86   $174.85   $174.90  
  Purchase #7 $218.59   6.473%   $232.7393   $232.74   $232.75   $232.70  
  7 purchase totals = $895.24       $975.6039   $975.60   $975.60   $975.60