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 $212.77   11.530%   $237.3024   $237.30   $237.30   $237.30  
  Purchase #2 $160.80   12.395%   $180.7312   $180.73   $180.75   $180.70  
  Purchase #3 $25.50   4.356%   $26.6108   $26.61   $26.60   $26.60  
  Purchase #4 $198.27   7.450%   $213.0411   $213.04   $213.05   $213.00  
  Purchase #5 $64.68   5.833%   $68.4528   $68.45   $68.45   $68.50  
  Purchase #6 $196.41   8.694%   $213.4859   $213.49   $213.50   $213.50  
  Purchase #7 $57.75   9.585%   $63.2853   $63.29   $63.30   $63.30  
  7 purchase totals = $916.18       $1,002.9095   $1,002.91   $1,002.95   $1,002.90