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 $240.74   10.780%   $266.6918   $266.69   $266.70   $266.70  
  Purchase #2 $160.55   5.478%   $169.3449   $169.34   $169.35   $169.30  
  Purchase #3 $215.51   7.634%   $231.962   $231.96   $231.95   $232.00  
  Purchase #4 $38.66   10.142%   $42.5809   $42.58   $42.60   $42.60  
  Purchase #5 $149.26   8.562%   $162.0396   $162.04   $162.05   $162.00  
  Purchase #6 $167.87   7.761%   $180.8984   $180.90   $180.90   $180.90  
  Purchase #7 $44.82   10.739%   $49.6332   $49.63   $49.65   $49.60  
  7 purchase totals = $1,017.41       $1,103.1508   $1,103.14   $1,103.20   $1,103.10