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 $68.62   4.724%   $71.8616   $71.86   $71.85   $71.90  
  Purchase #2 $215.76   11.645%   $240.8853   $240.89   $240.90   $240.90  
  Purchase #3 $221.29   6.221%   $235.0565   $235.06   $235.05   $235.10  
  Purchase #4 $212.71   11.481%   $237.1312   $237.13   $237.15   $237.10  
  Purchase #5 $81.95   8.449%   $88.874   $88.87   $88.85   $88.90  
  Purchase #6 $58.51   9.302%   $63.9526   $63.95   $63.95   $64.00  
  Purchase #7 $118.77   4.871%   $124.5553   $124.56   $124.55   $124.60  
  7 purchase totals = $977.61       $1,062.3165   $1,062.32   $1,062.30   $1,062.50