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 $200.35   13.163%   $226.7221   $226.72   $226.70   $226.70  
  Purchase #2 $59.57   12.819%   $67.2063   $67.21   $67.20   $67.20  
  Purchase #3 $110.40   11.837%   $123.468   $123.47   $123.45   $123.50  
  Purchase #4 $169.50   8.523%   $183.9465   $183.95   $183.95   $183.90  
  Purchase #5 $207.49   11.660%   $231.6833   $231.68   $231.70   $231.70  
  Purchase #6 $142.47   5.724%   $150.625   $150.63   $150.65   $150.60  
  Purchase #7 $60.71   9.524%   $66.492   $66.49   $66.50   $66.50  
  7 purchase totals = $950.49       $1,050.1432   $1,050.15   $1,050.15   $1,050.10