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 $92.84   4.348%   $96.8767   $96.88   $96.90   $96.90  
  Purchase #2 $206.86   9.648%   $226.8179   $226.82   $226.80   $226.80  
  Purchase #3 $202.52   13.159%   $229.1696   $229.17   $229.15   $229.20  
  Purchase #4 $243.26   7.128%   $260.5996   $260.60   $260.60   $260.60  
  Purchase #5 $169.61   13.455%   $192.431   $192.43   $192.45   $192.40  
  Purchase #6 $63.57   13.646%   $72.2448   $72.24   $72.25   $72.20  
  Purchase #7 $191.93   7.588%   $206.4936   $206.49   $206.50   $206.50  
  7 purchase totals = $1,170.59       $1,284.6332   $1,284.63   $1,284.65   $1,284.60