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 $209.46   11.103%   $232.7163   $232.72   $232.70   $232.70  
  Purchase #2 $183.49   5.487%   $193.5581   $193.56   $193.55   $193.60  
  Purchase #3 $84.79   7.414%   $91.0763   $91.08   $91.10   $91.10  
  Purchase #4 $227.84   8.299%   $246.7484   $246.75   $246.75   $246.70  
  Purchase #5 $148.29   3.863%   $154.0184   $154.02   $154.00   $154.00  
  Purchase #6 $99.74   11.807%   $111.5163   $111.52   $111.50   $111.50  
  Purchase #7 $248.36   6.543%   $264.6102   $264.61   $264.60   $264.60  
  7 purchase totals = $1,201.97       $1,294.2440   $1,294.26   $1,294.20   $1,294.20