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 $63.67   7.107%   $68.195   $68.20   $68.20   $68.20  
  Purchase #2 $151.65   8.623%   $164.7268   $164.73   $164.75   $164.70  
  Purchase #3 $190.51   10.418%   $210.3573   $210.36   $210.35   $210.40  
  Purchase #4 $185.53   8.121%   $200.5969   $200.60   $200.60   $200.60  
  Purchase #5 $84.32   10.402%   $93.091   $93.09   $93.10   $93.10  
  Purchase #6 $174.66   4.599%   $182.6926   $182.69   $182.70   $182.70  
  Purchase #7 $136.79   3.121%   $141.0592   $141.06   $141.05   $141.10  
  7 purchase totals = $987.13       $1,060.7188   $1,060.73   $1,060.75   $1,060.80