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 $49.95   13.659%   $56.7727   $56.77   $56.75   $56.80  
  Purchase #2 $179.92   9.132%   $196.3503   $196.35   $196.35   $196.40  
  Purchase #3 $163.25   11.271%   $181.6499   $181.65   $181.65   $181.60  
  Purchase #4 $122.72   9.222%   $134.0372   $134.04   $134.05   $134.00  
  Purchase #5 $211.39   12.476%   $237.763   $237.76   $237.75   $237.80  
  Purchase #6 $92.38   10.241%   $101.8406   $101.84   $101.85   $101.80  
  Purchase #7 $117.46   3.829%   $121.9575   $121.96   $121.95   $122.00  
  7 purchase totals = $937.07       $1,030.3712   $1,030.37   $1,030.35   $1,030.40