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 $192.82   5.547%   $203.5157   $203.52   $203.50   $203.50  
  Purchase #2 $50.26   6.712%   $53.6335   $53.63   $53.65   $53.60  
  Purchase #3 $121.32   10.103%   $133.577   $133.58   $133.60   $133.60  
  Purchase #4 $168.76   5.393%   $177.8612   $177.86   $177.85   $177.90  
  Purchase #5 $133.29   4.305%   $139.0281   $139.03   $139.05   $139.00  
  Purchase #6 $89.33   10.657%   $98.8499   $98.85   $98.85   $98.80  
  Purchase #7 $134.84   8.651%   $146.505   $146.51   $146.50   $146.50  
  7 purchase totals = $890.62       $952.9704   $952.98   $953.00   $952.90