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 $232.59   6.608%   $247.9595   $247.96   $247.95   $248.00  
  Purchase #2 $13.92   5.278%   $14.6547   $14.65   $14.65   $14.70  
  Purchase #3 $226.93   4.224%   $236.5155   $236.52   $236.50   $236.50  
  Purchase #4 $249.89   6.462%   $266.0379   $266.04   $266.05   $266.00  
  Purchase #5 $100.98   5.159%   $106.1896   $106.19   $106.20   $106.20  
  Purchase #6 $65.73   7.274%   $70.5112   $70.51   $70.50   $70.50  
  Purchase #7 $97.81   13.315%   $110.8334   $110.83   $110.85   $110.80  
  7 purchase totals = $987.85       $1,052.7018   $1,052.70   $1,052.70   $1,052.70