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 $119.33   3.797%   $123.861   $123.86   $123.85   $123.90  
  Purchase #2 $204.56   13.175%   $231.5108   $231.51   $231.50   $231.50  
  Purchase #3 $128.88   4.231%   $134.3329   $134.33   $134.35   $134.30  
  Purchase #4 $107.91   13.799%   $122.8005   $122.80   $122.80   $122.80  
  Purchase #5 $167.33   8.439%   $181.451   $181.45   $181.45   $181.50  
  Purchase #6 $137.99   12.516%   $155.2608   $155.26   $155.25   $155.30  
  Purchase #7 $47.46   11.114%   $52.7347   $52.73   $52.75   $52.70  
  7 purchase totals = $913.46       $1,001.9517   $1,001.94   $1,001.95   $1,002.00