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 $219.99   12.263%   $246.9674   $246.97   $246.95   $247.00  
  Purchase #2 $160.37   6.784%   $171.2495   $171.25   $171.25   $171.20  
  Purchase #3 $16.69   3.730%   $17.3125   $17.31   $17.30   $17.30  
  Purchase #4 $249.72   12.687%   $281.402   $281.40   $281.40   $281.40  
  Purchase #5 $190.40   7.673%   $205.0094   $205.01   $205.00   $205.00  
  Purchase #6 $47.48   4.419%   $49.5781   $49.58   $49.60   $49.60  
  Purchase #7 $210.73   11.310%   $234.5636   $234.56   $234.55   $234.60  
  7 purchase totals = $1,095.38       $1,206.0825   $1,206.08   $1,206.05   $1,206.10