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 $250.27   5.853%   $264.9183   $264.92   $264.90   $264.90  
  Purchase #2 $130.80   12.333%   $146.9316   $146.93   $146.95   $146.90  
  Purchase #3 $82.31   13.728%   $93.6095   $93.61   $93.60   $93.60  
  Purchase #4 $167.52   5.564%   $176.8408   $176.84   $176.85   $176.80  
  Purchase #5 $166.98   8.549%   $181.2551   $181.26   $181.25   $181.30  
  Purchase #6 $141.33   8.866%   $153.8603   $153.86   $153.85   $153.90  
  Purchase #7 $7.50   9.500%   $8.2125   $8.21   $8.20   $8.20  
  7 purchase totals = $946.71       $1,025.6281   $1,025.63   $1,025.60   $1,025.60