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 $22.74   12.686%   $25.6248   $25.62   $25.60   $25.60  
  Purchase #2 $247.72   11.747%   $276.8197   $276.82   $276.80   $276.80  
  Purchase #3 $86.55   13.187%   $97.9633   $97.96   $97.95   $98.00  
  Purchase #4 $168.86   6.163%   $179.2668   $179.27   $179.25   $179.30  
  Purchase #5 $206.40   6.433%   $219.6777   $219.68   $219.70   $219.70  
  Purchase #6 $118.84   13.344%   $134.698   $134.70   $134.70   $134.70  
  Purchase #7 $196.31   9.370%   $214.7042   $214.70   $214.70   $214.70  
  7 purchase totals = $1,047.42       $1,148.7545   $1,148.75   $1,148.70   $1,148.80