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 $172.35   8.327%   $186.7016   $186.70   $186.70   $186.70  
  Purchase #2 $211.27   11.331%   $235.209   $235.21   $235.20   $235.20  
  Purchase #3 $193.33   11.455%   $215.476   $215.48   $215.50   $215.50  
  Purchase #4 $43.41   10.239%   $47.8547   $47.85   $47.85   $47.90  
  Purchase #5 $247.69   10.619%   $273.9922   $273.99   $274.00   $274.00  
  Purchase #6 $84.60   11.644%   $94.4508   $94.45   $94.45   $94.50  
  Purchase #7 $158.46   12.556%   $178.3562   $178.36   $178.35   $178.40  
  7 purchase totals = $1,111.11       $1,232.0405   $1,232.04   $1,232.05   $1,232.20