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 $195.88   6.723%   $209.049   $209.05   $209.05   $209.00  
  Purchase #2 $48.81   7.633%   $52.5357   $52.54   $52.55   $52.50  
  Purchase #3 $99.70   5.581%   $105.2643   $105.26   $105.25   $105.30  
  Purchase #4 $85.90   11.457%   $95.7416   $95.74   $95.75   $95.70  
  Purchase #5 $40.78   12.751%   $45.9799   $45.98   $46.00   $46.00  
  Purchase #6 $133.29   12.166%   $149.5061   $149.51   $149.50   $149.50  
  Purchase #7 $33.29   5.135%   $34.9994   $35.00   $35.00   $35.00  
  7 purchase totals = $637.65       $693.0760   $693.08   $693.10   $693.00