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 $97.68   8.676%   $106.1547   $106.15   $106.15   $106.20  
  Purchase #2 $223.42   5.611%   $235.9561   $235.96   $235.95   $236.00  
  Purchase #3 $244.93   9.158%   $267.3607   $267.36   $267.35   $267.40  
  Purchase #4 $73.69   13.554%   $83.6779   $83.68   $83.70   $83.70  
  Purchase #5 $20.69   3.758%   $21.4675   $21.47   $21.45   $21.50  
  Purchase #6 $148.32   11.132%   $164.831   $164.83   $164.85   $164.80  
  Purchase #7 $141.77   3.813%   $147.1757   $147.18   $147.20   $147.20  
  7 purchase totals = $950.50       $1,026.6236   $1,026.63   $1,026.65   $1,026.80