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 $181.63   9.691%   $199.2318   $199.23   $199.25   $199.20  
  Purchase #2 $228.60   6.442%   $243.3264   $243.33   $243.35   $243.30  
  Purchase #3 $237.88   7.294%   $255.231   $255.23   $255.25   $255.20  
  Purchase #4 $238.55   6.784%   $254.7332   $254.73   $254.75   $254.70  
  Purchase #5 $215.82   5.560%   $227.8196   $227.82   $227.80   $227.80  
  Purchase #6 $195.70   6.424%   $208.2718   $208.27   $208.25   $208.30  
  Purchase #7 $160.80   4.399%   $167.8736   $167.87   $167.85   $167.90  
  7 purchase totals = $1,458.98       $1,556.4874   $1,556.48   $1,556.50   $1,556.40