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 $177.27   12.110%   $198.7374   $198.74   $198.75   $198.70  
  Purchase #2 $23.46   5.480%   $24.7456   $24.75   $24.75   $24.70  
  Purchase #3 $169.70   6.297%   $180.386   $180.39   $180.40   $180.40  
  Purchase #4 $237.42   12.560%   $267.24   $267.24   $267.25   $267.20  
  Purchase #5 $101.29   13.376%   $114.8386   $114.84   $114.85   $114.80  
  Purchase #6 $223.44   7.621%   $240.4684   $240.47   $240.45   $240.50  
  Purchase #7 $214.58   9.614%   $235.2097   $235.21   $235.20   $235.20  
  7 purchase totals = $1,147.16       $1,261.6257   $1,261.64   $1,261.65   $1,261.50