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 $165.99   7.605%   $178.6135   $178.61   $178.60   $178.60  
  Purchase #2 $62.48   11.815%   $69.862   $69.86   $69.85   $69.90  
  Purchase #3 $17.83   8.605%   $19.3643   $19.36   $19.35   $19.40  
  Purchase #4 $70.93   10.461%   $78.35   $78.35   $78.35   $78.40  
  Purchase #5 $240.74   11.729%   $268.9764   $268.98   $269.00   $269.00  
  Purchase #6 $41.41   8.844%   $45.0723   $45.07   $45.05   $45.10  
  Purchase #7 $213.27   9.854%   $234.2856   $234.29   $234.30   $234.30  
  7 purchase totals = $812.65       $894.5241   $894.52   $894.50   $894.70