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 $181.89   10.484%   $200.9593   $200.96   $200.95   $201.00  
  Purchase #2 $82.67   12.186%   $92.7442   $92.74   $92.75   $92.70  
  Purchase #3 $213.55   10.303%   $235.5521   $235.55   $235.55   $235.60  
  Purchase #4 $47.93   13.185%   $54.2496   $54.25   $54.25   $54.20  
  Purchase #5 $220.79   12.730%   $248.8966   $248.90   $248.90   $248.90  
  Purchase #6 $57.54   12.646%   $64.8165   $64.82   $64.80   $64.80  
  Purchase #7 $117.59   11.587%   $131.2152   $131.22   $131.20   $131.20  
  7 purchase totals = $921.96       $1,028.4335   $1,028.44   $1,028.40   $1,028.40