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 $216.31   7.865%   $233.3228   $233.32   $233.30   $233.30  
  Purchase #2 $25.31   8.433%   $27.4444   $27.44   $27.45   $27.40  
  Purchase #3 $181.46   7.769%   $195.5576   $195.56   $195.55   $195.60  
  Purchase #4 $219.84   13.600%   $249.7382   $249.74   $249.75   $249.70  
  Purchase #5 $192.99   11.822%   $215.8053   $215.81   $215.80   $215.80  
  Purchase #6 $98.83   8.389%   $107.1208   $107.12   $107.10   $107.10  
  Purchase #7 $58.68   12.264%   $65.8765   $65.88   $65.90   $65.90  
  7 purchase totals = $993.42       $1,094.8656   $1,094.87   $1,094.85   $1,094.80