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 $234.68   8.133%   $253.7665   $253.77   $253.75   $253.80  
  Purchase #2 $71.32   3.282%   $73.6607   $73.66   $73.65   $73.70  
  Purchase #3 $20.90   7.768%   $22.5235   $22.52   $22.50   $22.50  
  Purchase #4 $126.39   5.295%   $133.0824   $133.08   $133.10   $133.10  
  Purchase #5 $120.71   9.182%   $131.7936   $131.79   $131.80   $131.80  
  Purchase #6 $186.55   11.861%   $208.6767   $208.68   $208.70   $208.70  
  Purchase #7 $168.58   8.678%   $183.2094   $183.21   $183.20   $183.20  
  7 purchase totals = $929.13       $1,006.7128   $1,006.71   $1,006.70   $1,006.80