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 $88.29   8.201%   $95.5307   $95.53   $95.55   $95.50  
  Purchase #2 $38.67   8.254%   $41.8618   $41.86   $41.85   $41.90  
  Purchase #3 $20.54   5.686%   $21.7079   $21.71   $21.70   $21.70  
  Purchase #4 $160.37   9.216%   $175.1497   $175.15   $175.15   $175.10  
  Purchase #5 $206.50   9.677%   $226.483   $226.48   $226.50   $226.50  
  Purchase #6 $102.39   4.647%   $107.1481   $107.15   $107.15   $107.10  
  Purchase #7 $136.99   7.750%   $147.6067   $147.61   $147.60   $147.60  
  7 purchase totals = $753.75       $815.4879   $815.49   $815.50   $815.40