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 $62.86   13.487%   $71.3379   $71.34   $71.35   $71.30  
  Purchase #2 $181.51   7.789%   $195.6478   $195.65   $195.65   $195.60  
  Purchase #3 $93.25   7.154%   $99.9211   $99.92   $99.90   $99.90  
  Purchase #4 $60.58   11.664%   $67.6461   $67.65   $67.65   $67.60  
  Purchase #5 $114.91   7.649%   $123.6995   $123.70   $123.70   $123.70  
  Purchase #6 $80.95   8.843%   $88.1084   $88.11   $88.10   $88.10  
  Purchase #7 $79.33   6.174%   $84.2278   $84.23   $84.25   $84.20  
  7 purchase totals = $673.39       $730.5886   $730.60   $730.60   $730.40