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 $71.34   8.288%   $77.2527   $77.25   $77.25   $77.30  
  Purchase #2 $148.85   7.486%   $159.9929   $159.99   $160.00   $160.00  
  Purchase #3 $165.42   6.589%   $176.3195   $176.32   $176.30   $176.30  
  Purchase #4 $209.57   11.473%   $233.614   $233.61   $233.60   $233.60  
  Purchase #5 $242.65   6.861%   $259.2982   $259.30   $259.30   $259.30  
  Purchase #6 $201.46   12.495%   $226.6324   $226.63   $226.65   $226.60  
  Purchase #7 $245.55   9.437%   $268.7226   $268.72   $268.70   $268.70  
  7 purchase totals = $1,284.84       $1,401.8323   $1,401.82   $1,401.80   $1,401.80