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 $180.31   5.329%   $189.9187   $189.92   $189.90   $189.90  
  Purchase #2 $221.97   12.285%   $249.239   $249.24   $249.25   $249.20  
  Purchase #3 $222.69   10.189%   $245.3799   $245.38   $245.40   $245.40  
  Purchase #4 $84.83   4.155%   $88.3547   $88.35   $88.35   $88.40  
  Purchase #5 $36.59   12.647%   $41.2175   $41.22   $41.20   $41.20  
  Purchase #6 $94.29   7.222%   $101.0996   $101.10   $101.10   $101.10  
  Purchase #7 $88.68   9.182%   $96.8226   $96.82   $96.80   $96.80  
  7 purchase totals = $929.36       $1,012.0320   $1,012.03   $1,012.00   $1,012.00