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 $53.88   13.707%   $61.2653   $61.27   $61.25   $61.30  
  Purchase #2 $247.87   7.400%   $266.2124   $266.21   $266.20   $266.20  
  Purchase #3 $222.63   6.121%   $236.2572   $236.26   $236.25   $236.30  
  Purchase #4 $91.61   11.605%   $102.2413   $102.24   $102.25   $102.20  
  Purchase #5 $194.40   12.167%   $218.0526   $218.05   $218.05   $218.10  
  Purchase #6 $45.42   7.364%   $48.7647   $48.76   $48.75   $48.80  
  Purchase #7 $240.39   3.294%   $248.3084   $248.31   $248.30   $248.30  
  7 purchase totals = $1,096.20       $1,181.1019   $1,181.10   $1,181.05   $1,181.20