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 $235.45   12.459%   $264.7847   $264.78   $264.80   $264.80  
  Purchase #2 $87.79   8.162%   $94.9554   $94.96   $94.95   $95.00  
  Purchase #3 $139.63   12.737%   $157.4147   $157.41   $157.40   $157.40  
  Purchase #4 $244.57   7.835%   $263.7321   $263.73   $263.75   $263.70  
  Purchase #5 $161.89   4.419%   $169.0439   $169.04   $169.05   $169.00  
  Purchase #6 $136.68   6.792%   $145.9633   $145.96   $145.95   $146.00  
  Purchase #7 $22.85   4.602%   $23.9016   $23.90   $23.90   $23.90  
  7 purchase totals = $1,028.86       $1,119.7957   $1,119.78   $1,119.80   $1,119.80