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 $75.53   11.173%   $83.969   $83.97   $83.95   $84.00  
  Purchase #2 $211.67   9.138%   $231.0124   $231.01   $231.00   $231.00  
  Purchase #3 $58.95   5.737%   $62.332   $62.33   $62.35   $62.30  
  Purchase #4 $114.85   5.114%   $120.7234   $120.72   $120.70   $120.70  
  Purchase #5 $99.99   3.392%   $103.3817   $103.38   $103.40   $103.40  
  Purchase #6 $176.40   11.859%   $197.3193   $197.32   $197.30   $197.30  
  Purchase #7 $237.49   12.213%   $266.4947   $266.49   $266.50   $266.50  
  7 purchase totals = $974.88       $1,065.2325   $1,065.22   $1,065.20   $1,065.20