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 $197.48   12.789%   $222.7357   $222.74   $222.75   $222.70  
  Purchase #2 $105.49   9.788%   $115.8154   $115.82   $115.80   $115.80  
  Purchase #3 $70.44   11.456%   $78.5096   $78.51   $78.50   $78.50  
  Purchase #4 $111.55   4.420%   $116.4805   $116.48   $116.50   $116.50  
  Purchase #5 $56.62   7.278%   $60.7408   $60.74   $60.75   $60.70  
  Purchase #6 $23.96   3.222%   $24.732   $24.73   $24.75   $24.70  
  Purchase #7 $156.85   3.788%   $162.7915   $162.79   $162.80   $162.80  
  7 purchase totals = $722.39       $781.8055   $781.81   $781.85   $781.70