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 $230.55   7.201%   $247.1519   $247.15   $247.15   $247.20  
  Purchase #2 $179.98   4.640%   $188.3311   $188.33   $188.35   $188.30  
  Purchase #3 $80.97   9.527%   $88.684   $88.68   $88.70   $88.70  
  Purchase #4 $175.35   7.181%   $187.9419   $187.94   $187.95   $187.90  
  Purchase #5 $94.36   3.248%   $97.4248   $97.42   $97.40   $97.40  
  Purchase #6 $118.61   13.408%   $134.5132   $134.51   $134.50   $134.50  
  Purchase #7 $178.51   7.672%   $192.2053   $192.21   $192.20   $192.20  
  7 purchase totals = $1,058.33       $1,136.2522   $1,136.24   $1,136.25   $1,136.20