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 $220.81   10.458%   $243.9023   $243.90   $243.90   $243.90  
  Purchase #2 $95.58   12.369%   $107.4023   $107.40   $107.40   $107.40  
  Purchase #3 $71.37   6.492%   $76.0033   $76.00   $76.00   $76.00  
  Purchase #4 $170.32   4.183%   $177.4445   $177.44   $177.45   $177.40  
  Purchase #5 $183.49   11.517%   $204.6225   $204.62   $204.60   $204.60  
  Purchase #6 $97.67   7.514%   $105.0089   $105.01   $105.00   $105.00  
  Purchase #7 $116.70   5.481%   $123.0963   $123.10   $123.10   $123.10  
  7 purchase totals = $955.94       $1,037.4801   $1,037.47   $1,037.45   $1,037.40