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 $69.32   8.838%   $75.4465   $75.45   $75.45   $75.40  
  Purchase #2 $75.82   10.745%   $83.9669   $83.97   $83.95   $84.00  
  Purchase #3 $244.25   7.433%   $262.4051   $262.41   $262.40   $262.40  
  Purchase #4 $22.33   6.783%   $23.8446   $23.84   $23.85   $23.80  
  Purchase #5 $244.27   7.419%   $262.3924   $262.39   $262.40   $262.40  
  Purchase #6 $236.25   12.803%   $266.4971   $266.50   $266.50   $266.50  
  Purchase #7 $160.90   7.310%   $172.6618   $172.66   $172.65   $172.70  
  7 purchase totals = $1,053.14       $1,147.2144   $1,147.22   $1,147.20   $1,147.20