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 $119.86   4.191%   $124.8833   $124.88   $124.90   $124.90  
  Purchase #2 $26.77   11.149%   $29.7546   $29.75   $29.75   $29.80  
  Purchase #3 $65.71   6.480%   $69.968   $69.97   $69.95   $70.00  
  Purchase #4 $203.77   4.273%   $212.4771   $212.48   $212.50   $212.50  
  Purchase #5 $223.55   13.463%   $253.6465   $253.65   $253.65   $253.60  
  Purchase #6 $234.55   6.562%   $249.9412   $249.94   $249.95   $249.90  
  Purchase #7 $56.97   12.126%   $63.8782   $63.88   $63.90   $63.90  
  7 purchase totals = $931.18       $1,004.5489   $1,004.55   $1,004.60   $1,004.60