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 $199.50   10.550%   $220.5473   $220.55   $220.55   $220.50  
  Purchase #2 $132.80   4.512%   $138.7919   $138.79   $138.80   $138.80  
  Purchase #3 $207.98   10.266%   $229.3312   $229.33   $229.35   $229.30  
  Purchase #4 $14.83   8.505%   $16.0913   $16.09   $16.10   $16.10  
  Purchase #5 $133.83   12.161%   $150.1051   $150.11   $150.10   $150.10  
  Purchase #6 $217.66   7.817%   $234.6745   $234.67   $234.65   $234.70  
  Purchase #7 $124.62   12.239%   $139.8722   $139.87   $139.85   $139.90  
  7 purchase totals = $1,031.22       $1,129.4135   $1,129.41   $1,129.40   $1,129.40