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 $108.68   11.672%   $121.3651   $121.37   $121.35   $121.40  
  Purchase #2 $179.68   9.675%   $197.064   $197.06   $197.05   $197.10  
  Purchase #3 $198.63   9.602%   $217.7025   $217.70   $217.70   $217.70  
  Purchase #4 $181.44   9.358%   $198.4192   $198.42   $198.40   $198.40  
  Purchase #5 $30.31   4.338%   $31.6248   $31.62   $31.60   $31.60  
  Purchase #6 $91.86   11.415%   $102.3458   $102.35   $102.35   $102.30  
  Purchase #7 $216.25   13.820%   $246.1358   $246.14   $246.15   $246.10  
  7 purchase totals = $1,006.85       $1,114.6572   $1,114.66   $1,114.60   $1,114.60