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 $52.86   7.436%   $56.7907   $56.79   $56.80   $56.80  
  Purchase #2 $211.54   12.605%   $238.2046   $238.20   $238.20   $238.20  
  Purchase #3 $105.41   9.225%   $115.1341   $115.13   $115.15   $115.10  
  Purchase #4 $222.50   4.327%   $232.1276   $232.13   $232.15   $232.10  
  Purchase #5 $195.73   8.293%   $211.9619   $211.96   $211.95   $212.00  
  Purchase #6 $99.59   4.158%   $103.731   $103.73   $103.75   $103.70  
  Purchase #7 $62.75   6.636%   $66.9141   $66.91   $66.90   $66.90  
  7 purchase totals = $950.38       $1,024.8640   $1,024.85   $1,024.90   $1,024.80