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 $235.98   3.831%   $245.0204   $245.02   $245.00   $245.00  
  Purchase #2 $89.85   11.304%   $100.0066   $100.01   $100.00   $100.00  
  Purchase #3 $27.80   6.623%   $29.6412   $29.64   $29.65   $29.60  
  Purchase #4 $84.64   7.173%   $90.7112   $90.71   $90.70   $90.70  
  Purchase #5 $176.27   6.109%   $187.0383   $187.04   $187.05   $187.00  
  Purchase #6 $211.31   10.119%   $232.6925   $232.69   $232.70   $232.70  
  Purchase #7 $164.44   5.789%   $173.9594   $173.96   $173.95   $174.00  
  7 purchase totals = $990.29       $1,059.0696   $1,059.07   $1,059.05   $1,059.00