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 $31.51   8.207%   $34.096   $34.10   $34.10   $34.10  
  Purchase #2 $115.50   5.453%   $121.7982   $121.80   $121.80   $121.80  
  Purchase #3 $70.61   9.524%   $77.3349   $77.33   $77.35   $77.30  
  Purchase #4 $231.86   4.280%   $241.7836   $241.78   $241.80   $241.80  
  Purchase #5 $65.84   8.777%   $71.6188   $71.62   $71.60   $71.60  
  Purchase #6 $208.42   6.672%   $222.3258   $222.33   $222.35   $222.30  
  Purchase #7 $235.92   11.108%   $262.126   $262.13   $262.15   $262.10  
  7 purchase totals = $959.66       $1,031.0833   $1,031.09   $1,031.15   $1,031.00