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 $89.95   12.277%   $100.9932   $100.99   $101.00   $101.00  
  Purchase #2 $211.97   13.287%   $240.1345   $240.13   $240.15   $240.10  
  Purchase #3 $186.98   6.252%   $198.67   $198.67   $198.65   $198.70  
  Purchase #4 $167.76   8.188%   $181.4962   $181.50   $181.50   $181.50  
  Purchase #5 $176.78   10.619%   $195.5523   $195.55   $195.55   $195.60  
  Purchase #6 $128.61   11.598%   $143.5262   $143.53   $143.55   $143.50  
  Purchase #7 $83.66   11.214%   $93.0416   $93.04   $93.05   $93.00  
  7 purchase totals = $1,045.71       $1,153.4140   $1,153.41   $1,153.45   $1,153.40