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 $21.66   4.613%   $22.6592   $22.66   $22.65   $22.70  
  Purchase #2 $56.59   10.551%   $62.5608   $62.56   $62.55   $62.60  
  Purchase #3 $84.61   12.761%   $95.4071   $95.41   $95.40   $95.40  
  Purchase #4 $196.42   3.669%   $203.6266   $203.63   $203.65   $203.60  
  Purchase #5 $159.73   13.710%   $181.629   $181.63   $181.65   $181.60  
  Purchase #6 $244.31   10.476%   $269.9039   $269.90   $269.90   $269.90  
  Purchase #7 $178.55   5.213%   $187.8578   $187.86   $187.85   $187.90  
  7 purchase totals = $941.87       $1,023.6444   $1,023.65   $1,023.65   $1,023.70