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 $84.99   12.704%   $95.7871   $95.79   $95.80   $95.80  
  Purchase #2 $222.87   6.297%   $236.9041   $236.90   $236.90   $236.90  
  Purchase #3 $78.93   6.822%   $84.3146   $84.31   $84.30   $84.30  
  Purchase #4 $220.72   9.871%   $242.5073   $242.51   $242.50   $242.50  
  Purchase #5 $189.55   10.603%   $209.648   $209.65   $209.65   $209.60  
  Purchase #6 $35.96   4.778%   $37.6782   $37.68   $37.70   $37.70  
  Purchase #7 $110.49   6.130%   $117.263   $117.26   $117.25   $117.30  
  7 purchase totals = $943.51       $1,024.1023   $1,024.10   $1,024.10   $1,024.10