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 $23.53   4.589%   $24.6098   $24.61   $24.60   $24.60  
  Purchase #2 $165.72   8.493%   $179.7946   $179.79   $179.80   $179.80  
  Purchase #3 $217.46   9.868%   $238.919   $238.92   $238.90   $238.90  
  Purchase #4 $45.33   4.460%   $47.3517   $47.35   $47.35   $47.40  
  Purchase #5 $11.73   5.424%   $12.3662   $12.37   $12.35   $12.40  
  Purchase #6 $235.50   8.473%   $255.4539   $255.45   $255.45   $255.50  
  Purchase #7 $212.59   11.345%   $236.7083   $236.71   $236.70   $236.70  
  7 purchase totals = $911.86       $995.2035   $995.20   $995.15   $995.30