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 $78.53   10.697%   $86.9304   $86.93   $86.95   $86.90  
  Purchase #2 $127.38   6.161%   $135.2279   $135.23   $135.25   $135.20  
  Purchase #3 $88.94   11.700%   $99.346   $99.35   $99.35   $99.30  
  Purchase #4 $197.79   7.718%   $213.0554   $213.06   $213.05   $213.10  
  Purchase #5 $120.57   13.328%   $136.6396   $136.64   $136.65   $136.60  
  Purchase #6 $91.35   12.334%   $102.6171   $102.62   $102.60   $102.60  
  Purchase #7 $175.93   8.691%   $191.2201   $191.22   $191.20   $191.20  
  7 purchase totals = $880.49       $965.0365   $965.05   $965.05   $964.90