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 $61.94   7.487%   $66.5774   $66.58   $66.60   $66.60  
  Purchase #2 $169.82   9.191%   $185.4282   $185.43   $185.45   $185.40  
  Purchase #3 $34.78   10.276%   $38.354   $38.35   $38.35   $38.40  
  Purchase #4 $204.35   13.745%   $232.4379   $232.44   $232.45   $232.40  
  Purchase #5 $243.97   7.137%   $261.3821   $261.38   $261.40   $261.40  
  Purchase #6 $163.90   3.150%   $169.0629   $169.06   $169.05   $169.10  
  Purchase #7 $97.77   12.828%   $110.3119   $110.31   $110.30   $110.30  
  7 purchase totals = $976.53       $1,063.5544   $1,063.55   $1,063.60   $1,063.60