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 $94.33   4.212%   $98.3032   $98.30   $98.30   $98.30  
  Purchase #2 $181.70   11.838%   $203.2096   $203.21   $203.20   $203.20  
  Purchase #3 $190.92   7.621%   $205.47   $205.47   $205.45   $205.50  
  Purchase #4 $216.89   5.205%   $228.1791   $228.18   $228.20   $228.20  
  Purchase #5 $129.65   6.204%   $137.6935   $137.69   $137.70   $137.70  
  Purchase #6 $106.66   6.572%   $113.6697   $113.67   $113.65   $113.70  
  Purchase #7 $241.93   3.855%   $251.2564   $251.26   $251.25   $251.30  
  7 purchase totals = $1,162.08       $1,237.7815   $1,237.78   $1,237.75   $1,237.90