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 $25.56   3.532%   $26.4628   $26.46   $26.45   $26.50  
  Purchase #2 $218.90   11.169%   $243.3489   $243.35   $243.35   $243.30  
  Purchase #3 $207.81   12.103%   $232.9612   $232.96   $232.95   $233.00  
  Purchase #4 $233.44   3.254%   $241.0361   $241.04   $241.05   $241.00  
  Purchase #5 $177.66   5.453%   $187.3478   $187.35   $187.35   $187.30  
  Purchase #6 $183.57   8.839%   $199.7958   $199.80   $199.80   $199.80  
  Purchase #7 $189.90   3.472%   $196.4933   $196.49   $196.50   $196.50  
  7 purchase totals = $1,236.84       $1,327.4459   $1,327.45   $1,327.45   $1,327.40