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 $214.67   5.637%   $226.7709   $226.77   $226.75   $226.80  
  Purchase #2 $72.27   3.739%   $74.9722   $74.97   $74.95   $75.00  
  Purchase #3 $243.31   13.311%   $275.697   $275.70   $275.70   $275.70  
  Purchase #4 $118.41   11.489%   $132.0141   $132.01   $132.00   $132.00  
  Purchase #5 $168.77   5.674%   $178.346   $178.35   $178.35   $178.30  
  Purchase #6 $178.36   3.462%   $184.5348   $184.53   $184.55   $184.50  
  Purchase #7 $28.39   11.116%   $31.5458   $31.55   $31.55   $31.50  
  7 purchase totals = $1,024.18       $1,103.8808   $1,103.88   $1,103.85   $1,103.80