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 $246.95   7.217%   $264.7724   $264.77   $264.75   $264.80  
  Purchase #2 $240.60   10.126%   $264.9632   $264.96   $264.95   $265.00  
  Purchase #3 $165.55   11.781%   $185.0534   $185.05   $185.05   $185.10  
  Purchase #4 $54.96   9.736%   $60.3109   $60.31   $60.30   $60.30  
  Purchase #5 $77.70   8.166%   $84.045   $84.05   $84.05   $84.00  
  Purchase #6 $195.43   7.247%   $209.5928   $209.59   $209.60   $209.60  
  Purchase #7 $57.25   13.349%   $64.8923   $64.89   $64.90   $64.90  
  7 purchase totals = $1,038.44       $1,133.6300   $1,133.62   $1,133.60   $1,133.70