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 $204.34   10.831%   $226.4721   $226.47   $226.45   $226.50  
  Purchase #2 $15.34   8.504%   $16.6445   $16.64   $16.65   $16.60  
  Purchase #3 $153.63   13.379%   $174.1842   $174.18   $174.20   $174.20  
  Purchase #4 $103.79   6.860%   $110.91   $110.91   $110.90   $110.90  
  Purchase #5 $51.69   4.411%   $53.97   $53.97   $53.95   $54.00  
  Purchase #6 $88.96   4.828%   $93.255   $93.26   $93.25   $93.30  
  Purchase #7 $211.37   13.819%   $240.5792   $240.58   $240.60   $240.60  
  7 purchase totals = $829.12       $916.0150   $916.01   $916.00   $916.10