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 $38.96   13.226%   $44.1128   $44.11   $44.10   $44.10  
  Purchase #2 $184.39   9.473%   $201.8573   $201.86   $201.85   $201.90  
  Purchase #3 $44.46   10.407%   $49.087   $49.09   $49.10   $49.10  
  Purchase #4 $248.66   5.796%   $263.0723   $263.07   $263.05   $263.10  
  Purchase #5 $63.98   5.199%   $67.3063   $67.31   $67.30   $67.30  
  Purchase #6 $25.44   7.166%   $27.263   $27.26   $27.25   $27.30  
  Purchase #7 $185.67   9.662%   $203.6094   $203.61   $203.60   $203.60  
  7 purchase totals = $791.56       $856.3081   $856.31   $856.25   $856.40