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 $108.82   4.517%   $113.7354   $113.74   $113.75   $113.70  
  Purchase #2 $224.95   13.291%   $254.8481   $254.85   $254.85   $254.80  
  Purchase #3 $92.98   6.112%   $98.6629   $98.66   $98.65   $98.70  
  Purchase #4 $163.81   4.163%   $170.6294   $170.63   $170.65   $170.60  
  Purchase #5 $221.93   8.406%   $240.5854   $240.59   $240.60   $240.60  
  Purchase #6 $119.89   8.373%   $129.9284   $129.93   $129.95   $129.90  
  Purchase #7 $52.88   13.690%   $60.1193   $60.12   $60.10   $60.10  
  7 purchase totals = $985.26       $1,068.5089   $1,068.52   $1,068.55   $1,068.40