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 $168.98   7.486%   $181.6298   $181.63   $181.65   $181.60  
  Purchase #2 $127.42   11.853%   $142.5231   $142.52   $142.50   $142.50  
  Purchase #3 $249.38   7.709%   $268.6047   $268.60   $268.60   $268.60  
  Purchase #4 $160.96   10.397%   $177.695   $177.70   $177.70   $177.70  
  Purchase #5 $218.57   4.475%   $228.351   $228.35   $228.35   $228.40  
  Purchase #6 $127.88   5.661%   $135.1193   $135.12   $135.10   $135.10  
  Purchase #7 $82.94   7.646%   $89.2816   $89.28   $89.30   $89.30  
  7 purchase totals = $1,136.13       $1,223.2045   $1,223.20   $1,223.20   $1,223.20