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 $68.65   12.224%   $77.0418   $77.04   $77.05   $77.00  
  Purchase #2 $187.40   10.424%   $206.9346   $206.93   $206.95   $206.90  
  Purchase #3 $126.73   13.382%   $143.689   $143.69   $143.70   $143.70  
  Purchase #4 $171.87   4.367%   $179.3756   $179.38   $179.40   $179.40  
  Purchase #5 $97.79   5.704%   $103.3679   $103.37   $103.35   $103.40  
  Purchase #6 $240.52   8.483%   $260.9233   $260.92   $260.90   $260.90  
  Purchase #7 $123.38   10.759%   $136.6545   $136.65   $136.65   $136.70  
  7 purchase totals = $1,016.34       $1,107.9867   $1,107.98   $1,108.00   $1,108.00