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 $58.59   7.857%   $63.1934   $63.19   $63.20   $63.20  
  Purchase #2 $235.45   4.126%   $245.1647   $245.16   $245.15   $245.20  
  Purchase #3 $243.79   6.459%   $259.5364   $259.54   $259.55   $259.50  
  Purchase #4 $20.29   5.620%   $21.4303   $21.43   $21.45   $21.40  
  Purchase #5 $176.95   5.167%   $186.093   $186.09   $186.10   $186.10  
  Purchase #6 $101.30   5.344%   $106.7135   $106.71   $106.70   $106.70  
  Purchase #7 $212.47   10.163%   $234.0633   $234.06   $234.05   $234.10  
  7 purchase totals = $1,048.84       $1,116.1946   $1,116.18   $1,116.20   $1,116.20