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 $160.94   8.129%   $174.0228   $174.02   $174.00   $174.00  
  Purchase #2 $67.93   12.427%   $76.3717   $76.37   $76.35   $76.40  
  Purchase #3 $237.49   9.301%   $259.5789   $259.58   $259.60   $259.60  
  Purchase #4 $105.74   8.414%   $114.637   $114.64   $114.65   $114.60  
  Purchase #5 $115.60   9.720%   $126.8363   $126.84   $126.85   $126.80  
  Purchase #6 $131.29   9.349%   $143.5643   $143.56   $143.55   $143.60  
  Purchase #7 $92.49   5.537%   $97.6112   $97.61   $97.60   $97.60  
  7 purchase totals = $911.48       $992.6222   $992.62   $992.60   $992.60