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 $172.39   12.664%   $194.2215   $194.22   $194.20   $194.20  
  Purchase #2 $77.49   6.632%   $82.6291   $82.63   $82.65   $82.60  
  Purchase #3 $196.40   11.522%   $219.0292   $219.03   $219.05   $219.00  
  Purchase #4 $86.63   6.683%   $92.4195   $92.42   $92.40   $92.40  
  Purchase #5 $66.29   10.238%   $73.0768   $73.08   $73.10   $73.10  
  Purchase #6 $202.84   6.585%   $216.197   $216.20   $216.20   $216.20  
  Purchase #7 $139.88   6.509%   $148.9848   $148.98   $149.00   $149.00  
  7 purchase totals = $941.92       $1,026.5579   $1,026.56   $1,026.60   $1,026.50