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 $71.27   5.713%   $75.3417   $75.34   $75.35   $75.30  
  Purchase #2 $108.92   8.695%   $118.3906   $118.39   $118.40   $118.40  
  Purchase #3 $112.81   10.436%   $124.5829   $124.58   $124.60   $124.60  
  Purchase #4 $188.25   3.105%   $194.0952   $194.10   $194.10   $194.10  
  Purchase #5 $149.78   4.685%   $156.7972   $156.80   $156.80   $156.80  
  Purchase #6 $243.93   5.623%   $257.6462   $257.65   $257.65   $257.60  
  Purchase #7 $148.41   5.211%   $156.1436   $156.14   $156.15   $156.10  
  7 purchase totals = $1,023.37       $1,082.9974   $1,083.00   $1,083.05   $1,082.90