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 $65.91   13.787%   $74.997   $75.00   $75.00   $75.00  
  Purchase #2 $211.44   7.792%   $227.9154   $227.92   $227.90   $227.90  
  Purchase #3 $86.98   4.267%   $90.6914   $90.69   $90.70   $90.70  
  Purchase #4 $85.71   3.331%   $88.565   $88.57   $88.55   $88.60  
  Purchase #5 $72.57   11.419%   $80.8568   $80.86   $80.85   $80.90  
  Purchase #6 $13.66   8.430%   $14.8115   $14.81   $14.80   $14.80  
  Purchase #7 $192.98   13.267%   $218.5827   $218.58   $218.60   $218.60  
  7 purchase totals = $729.25       $796.4198   $796.43   $796.40   $796.50