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 $186.86   13.855%   $212.7495   $212.75   $212.75   $212.70  
  Purchase #2 $201.64   4.493%   $210.6997   $210.70   $210.70   $210.70  
  Purchase #3 $79.62   12.151%   $89.2946   $89.29   $89.30   $89.30  
  Purchase #4 $102.53   4.594%   $107.2402   $107.24   $107.25   $107.20  
  Purchase #5 $51.31   6.129%   $54.4548   $54.45   $54.45   $54.50  
  Purchase #6 $169.82   4.594%   $177.6215   $177.62   $177.60   $177.60  
  Purchase #7 $8.59   7.574%   $9.2406   $9.24   $9.25   $9.20  
  7 purchase totals = $800.37       $861.3009   $861.29   $861.30   $861.20