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 $90.85   11.682%   $101.4631   $101.46   $101.45   $101.50  
  Purchase #2 $113.44   13.571%   $128.8349   $128.83   $128.85   $128.80  
  Purchase #3 $10.43   12.429%   $11.7263   $11.73   $11.75   $11.70  
  Purchase #4 $235.98   3.469%   $244.1661   $244.17   $244.15   $244.20  
  Purchase #5 $244.54   4.696%   $256.0236   $256.02   $256.00   $256.00  
  Purchase #6 $75.97   13.479%   $86.21   $86.21   $86.20   $86.20  
  Purchase #7 $177.95   4.780%   $186.456   $186.46   $186.45   $186.50  
  7 purchase totals = $949.16       $1,014.8800   $1,014.88   $1,014.85   $1,014.90