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 $57.89   9.736%   $63.5262   $63.53   $63.55   $63.50  
  Purchase #2 $197.68   4.460%   $206.4965   $206.50   $206.50   $206.50  
  Purchase #3 $41.71   9.576%   $45.7041   $45.70   $45.70   $45.70  
  Purchase #4 $227.60   8.527%   $247.0075   $247.01   $247.00   $247.00  
  Purchase #5 $72.39   4.723%   $75.809   $75.81   $75.80   $75.80  
  Purchase #6 $66.43   10.781%   $73.5918   $73.59   $73.60   $73.60  
  Purchase #7 $168.69   4.589%   $176.4312   $176.43   $176.45   $176.40  
  7 purchase totals = $832.39       $888.5663   $888.57   $888.60   $888.50