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 $89.84   6.859%   $96.0021   $96.00   $96.00   $96.00  
  Purchase #2 $211.79   10.273%   $233.5472   $233.55   $233.55   $233.50  
  Purchase #3 $105.84   7.522%   $113.8013   $113.80   $113.80   $113.80  
  Purchase #4 $152.62   12.564%   $171.7952   $171.80   $171.80   $171.80  
  Purchase #5 $167.97   12.552%   $189.0536   $189.05   $189.05   $189.10  
  Purchase #6 $45.95   4.432%   $47.9865   $47.99   $48.00   $48.00  
  Purchase #7 $54.91   4.562%   $57.415   $57.42   $57.40   $57.40  
  7 purchase totals = $828.92       $909.6009   $909.61   $909.60   $909.60