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 $59.72   3.428%   $61.7672   $61.77   $61.75   $61.80  
  Purchase #2 $10.87   10.200%   $11.9787   $11.98   $12.00   $12.00  
  Purchase #3 $238.41   9.750%   $261.655   $261.66   $261.65   $261.70  
  Purchase #4 $228.31   11.724%   $255.0771   $255.08   $255.10   $255.10  
  Purchase #5 $5.65   3.467%   $5.8459   $5.85   $5.85   $5.80  
  Purchase #6 $168.79   9.162%   $184.2545   $184.25   $184.25   $184.30  
  Purchase #7 $221.29   6.573%   $235.8354   $235.84   $235.85   $235.80  
  7 purchase totals = $933.04       $1,016.4138   $1,016.43   $1,016.45   $1,016.50