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 $148.93   11.176%   $165.5744   $165.57   $165.55   $165.60  
  Purchase #2 $97.58   9.212%   $106.5691   $106.57   $106.55   $106.60  
  Purchase #3 $48.87   11.811%   $54.642   $54.64   $54.65   $54.60  
  Purchase #4 $187.32   10.456%   $206.9062   $206.91   $206.90   $206.90  
  Purchase #5 $133.53   12.287%   $149.9368   $149.94   $149.95   $149.90  
  Purchase #6 $104.79   11.308%   $116.6397   $116.64   $116.65   $116.60  
  Purchase #7 $240.47   11.272%   $267.5758   $267.58   $267.60   $267.60  
  7 purchase totals = $961.49       $1,067.8440   $1,067.85   $1,067.85   $1,067.80