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 $98.39   9.219%   $107.4606   $107.46   $107.45   $107.50  
  Purchase #2 $8.31   11.516%   $9.267   $9.27   $9.25   $9.30  
  Purchase #3 $126.27   9.781%   $138.6205   $138.62   $138.60   $138.60  
  Purchase #4 $59.82   6.485%   $63.6993   $63.70   $63.70   $63.70  
  Purchase #5 $197.86   5.454%   $208.6513   $208.65   $208.65   $208.70  
  Purchase #6 $48.64   8.439%   $52.7447   $52.74   $52.75   $52.70  
  Purchase #7 $191.76   7.364%   $205.8812   $205.88   $205.90   $205.90  
  7 purchase totals = $731.05       $786.3246   $786.32   $786.30   $786.40