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 $81.93   12.704%   $92.3384   $92.34   $92.35   $92.30  
  Purchase #2 $165.65   3.644%   $171.6863   $171.69   $171.70   $171.70  
  Purchase #3 $43.96   9.611%   $48.185   $48.19   $48.20   $48.20  
  Purchase #4 $198.51   11.724%   $221.7833   $221.78   $221.80   $221.80  
  Purchase #5 $210.57   8.680%   $228.8475   $228.85   $228.85   $228.80  
  Purchase #6 $195.84   11.634%   $218.624   $218.62   $218.60   $218.60  
  Purchase #7 $124.88   10.632%   $138.1572   $138.16   $138.15   $138.20  
  7 purchase totals = $1,021.34       $1,119.6217   $1,119.63   $1,119.65   $1,119.60