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 $63.48   9.559%   $69.5481   $69.55   $69.55   $69.50  
  Purchase #2 $62.41   4.334%   $65.1148   $65.11   $65.10   $65.10  
  Purchase #3 $96.56   7.277%   $103.5867   $103.59   $103.60   $103.60  
  Purchase #4 $231.74   13.577%   $263.2033   $263.20   $263.20   $263.20  
  Purchase #5 $168.76   9.710%   $185.1466   $185.15   $185.15   $185.10  
  Purchase #6 $123.34   13.488%   $139.9761   $139.98   $140.00   $140.00  
  Purchase #7 $152.36   12.735%   $171.763   $171.76   $171.75   $171.80  
  7 purchase totals = $898.65       $998.3386   $998.34   $998.35   $998.30