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 $218.95   11.592%   $244.3307   $244.33   $244.35   $244.30  
  Purchase #2 $179.73   6.810%   $191.9696   $191.97   $191.95   $192.00  
  Purchase #3 $240.93   6.146%   $255.7376   $255.74   $255.75   $255.70  
  Purchase #4 $121.45   13.501%   $137.847   $137.85   $137.85   $137.80  
  Purchase #5 $28.92   6.189%   $30.7099   $30.71   $30.70   $30.70  
  Purchase #6 $120.39   4.864%   $126.2458   $126.25   $126.25   $126.20  
  Purchase #7 $25.98   6.339%   $27.6269   $27.63   $27.65   $27.60  
  7 purchase totals = $936.35       $1,014.4675   $1,014.48   $1,014.50   $1,014.30