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 $50.65   3.153%   $52.247   $52.25   $52.25   $52.20  
  Purchase #2 $210.75   7.224%   $225.9746   $225.97   $225.95   $226.00  
  Purchase #3 $204.74   13.111%   $231.5835   $231.58   $231.60   $231.60  
  Purchase #4 $87.34   11.556%   $97.433   $97.43   $97.45   $97.40  
  Purchase #5 $174.87   8.236%   $189.2723   $189.27   $189.25   $189.30  
  Purchase #6 $220.65   8.433%   $239.2574   $239.26   $239.25   $239.30  
  Purchase #7 $75.47   7.237%   $80.9318   $80.93   $80.95   $80.90  
  7 purchase totals = $1,024.47       $1,116.6996   $1,116.69   $1,116.70   $1,116.70