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 $204.96   13.845%   $233.3367   $233.34   $233.35   $233.30  
  Purchase #2 $121.97   11.874%   $136.4527   $136.45   $136.45   $136.50  
  Purchase #3 $74.25   9.229%   $81.1025   $81.10   $81.10   $81.10  
  Purchase #4 $110.44   11.483%   $123.1218   $123.12   $123.10   $123.10  
  Purchase #5 $160.79   7.663%   $173.1113   $173.11   $173.10   $173.10  
  Purchase #6 $244.83   3.247%   $252.7796   $252.78   $252.80   $252.80  
  Purchase #7 $23.95   9.396%   $26.2003   $26.20   $26.20   $26.20  
  7 purchase totals = $941.19       $1,026.1049   $1,026.10   $1,026.10   $1,026.10