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 $62.38   12.810%   $70.3709   $70.37   $70.35   $70.40  
  Purchase #2 $99.74   4.844%   $104.5714   $104.57   $104.55   $104.60  
  Purchase #3 $62.52   13.874%   $71.194   $71.19   $71.20   $71.20  
  Purchase #4 $216.34   8.107%   $233.8787   $233.88   $233.90   $233.90  
  Purchase #5 $12.74   10.386%   $14.0632   $14.06   $14.05   $14.10  
  Purchase #6 $204.64   4.446%   $213.7383   $213.74   $213.75   $213.70  
  Purchase #7 $13.70   11.227%   $15.2381   $15.24   $15.25   $15.20  
  7 purchase totals = $672.06       $723.0546   $723.05   $723.05   $723.10