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 $217.44   13.842%   $247.538   $247.54   $247.55   $247.50  
  Purchase #2 $115.91   3.357%   $119.8011   $119.80   $119.80   $119.80  
  Purchase #3 $200.40   11.576%   $223.5983   $223.60   $223.60   $223.60  
  Purchase #4 $176.66   8.163%   $191.0808   $191.08   $191.10   $191.10  
  Purchase #5 $185.33   5.613%   $195.7326   $195.73   $195.75   $195.70  
  Purchase #6 $51.83   5.714%   $54.7916   $54.79   $54.80   $54.80  
  Purchase #7 $30.52   12.819%   $34.4324   $34.43   $34.45   $34.40  
  7 purchase totals = $978.09       $1,066.9748   $1,066.97   $1,067.05   $1,066.90