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 $167.49   8.505%   $181.735   $181.74   $181.75   $181.70  
  Purchase #2 $23.42   13.635%   $26.6133   $26.61   $26.60   $26.60  
  Purchase #3 $57.52   11.356%   $64.052   $64.05   $64.05   $64.10  
  Purchase #4 $93.38   11.531%   $104.1476   $104.15   $104.15   $104.10  
  Purchase #5 $46.96   11.118%   $52.181   $52.18   $52.20   $52.20  
  Purchase #6 $5.59   8.485%   $6.0643   $6.06   $6.05   $6.10  
  Purchase #7 $165.35   10.742%   $183.1119   $183.11   $183.10   $183.10  
  7 purchase totals = $559.71       $617.9051   $617.90   $617.90   $617.90