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 $171.39   13.643%   $194.7727   $194.77   $194.75   $194.80  
  Purchase #2 $58.84   7.655%   $63.3442   $63.34   $63.35   $63.30  
  Purchase #3 $78.28   9.280%   $85.5444   $85.54   $85.55   $85.50  
  Purchase #4 $44.34   7.483%   $47.658   $47.66   $47.65   $47.70  
  Purchase #5 $221.57   8.479%   $240.3569   $240.36   $240.35   $240.40  
  Purchase #6 $246.98   6.106%   $262.0606   $262.06   $262.05   $262.10  
  Purchase #7 $224.79   9.757%   $246.7228   $246.72   $246.70   $246.70  
  7 purchase totals = $1,046.19       $1,140.4596   $1,140.45   $1,140.40   $1,140.50