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 $54.47   5.614%   $57.5279   $57.53   $57.55   $57.50  
  Purchase #2 $184.45   5.248%   $194.1299   $194.13   $194.15   $194.10  
  Purchase #3 $249.27   3.286%   $257.461   $257.46   $257.45   $257.50  
  Purchase #4 $185.36   12.781%   $209.0509   $209.05   $209.05   $209.10  
  Purchase #5 $235.90   3.216%   $243.4865   $243.49   $243.50   $243.50  
  Purchase #6 $25.71   5.812%   $27.2043   $27.20   $27.20   $27.20  
  Purchase #7 $233.83   6.140%   $248.1872   $248.19   $248.20   $248.20  
  7 purchase totals = $1,168.99       $1,237.0477   $1,237.05   $1,237.10   $1,237.10