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 $250.53   5.225%   $263.6202   $263.62   $263.60   $263.60  
  Purchase #2 $128.52   13.347%   $145.6736   $145.67   $145.65   $145.70  
  Purchase #3 $11.85   5.364%   $12.4856   $12.49   $12.50   $12.50  
  Purchase #4 $212.27   10.127%   $233.7666   $233.77   $233.75   $233.80  
  Purchase #5 $96.27   11.391%   $107.2361   $107.24   $107.25   $107.20  
  Purchase #6 $93.32   9.635%   $102.3114   $102.31   $102.30   $102.30  
  Purchase #7 $82.36   6.491%   $87.706   $87.71   $87.70   $87.70  
  7 purchase totals = $875.12       $952.7995   $952.81   $952.75   $952.80