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 $211.58   8.511%   $229.5876   $229.59   $229.60   $229.60  
  Purchase #2 $92.38   5.820%   $97.7565   $97.76   $97.75   $97.80  
  Purchase #3 $74.94   3.669%   $77.6895   $77.69   $77.70   $77.70  
  Purchase #4 $125.91   11.841%   $140.819   $140.82   $140.80   $140.80  
  Purchase #5 $186.26   5.680%   $196.8396   $196.84   $196.85   $196.80  
  Purchase #6 $243.28   6.740%   $259.6771   $259.68   $259.70   $259.70  
  Purchase #7 $44.72   8.303%   $48.4331   $48.43   $48.45   $48.40  
  7 purchase totals = $979.07       $1,050.8024   $1,050.81   $1,050.85   $1,050.80