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 $224.65   8.834%   $244.4956   $244.50   $244.50   $244.50  
  Purchase #2 $30.83   12.340%   $34.6344   $34.63   $34.65   $34.60  
  Purchase #3 $75.94   5.535%   $80.1433   $80.14   $80.15   $80.10  
  Purchase #4 $169.71   6.774%   $181.2062   $181.21   $181.20   $181.20  
  Purchase #5 $189.97   11.712%   $212.2193   $212.22   $212.20   $212.20  
  Purchase #6 $221.50   6.459%   $235.8067   $235.81   $235.80   $235.80  
  Purchase #7 $54.99   12.562%   $61.8978   $61.90   $61.90   $61.90  
  7 purchase totals = $967.59       $1,050.4033   $1,050.41   $1,050.40   $1,050.30