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 $62.74   6.796%   $67.0038   $67.00   $67.00   $67.00  
  Purchase #2 $199.82   13.440%   $226.6758   $226.68   $226.70   $226.70  
  Purchase #3 $176.53   11.321%   $196.515   $196.52   $196.50   $196.50  
  Purchase #4 $124.81   7.756%   $134.4903   $134.49   $134.50   $134.50  
  Purchase #5 $87.62   11.284%   $97.507   $97.51   $97.50   $97.50  
  Purchase #6 $90.41   11.741%   $101.025   $101.03   $101.05   $101.00  
  Purchase #7 $210.69   5.823%   $222.9585   $222.96   $222.95   $223.00  
  7 purchase totals = $952.62       $1,046.1754   $1,046.19   $1,046.20   $1,046.20