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 $219.95   13.227%   $249.0428   $249.04   $249.05   $249.00  
  Purchase #2 $221.52   12.390%   $248.9663   $248.97   $248.95   $249.00  
  Purchase #3 $233.26   5.580%   $246.2759   $246.28   $246.30   $246.30  
  Purchase #4 $206.89   12.611%   $232.9809   $232.98   $233.00   $233.00  
  Purchase #5 $174.45   3.730%   $180.957   $180.96   $180.95   $181.00  
  Purchase #6 $198.32   12.133%   $222.3822   $222.38   $222.40   $222.40  
  Purchase #7 $12.85   5.851%   $13.6019   $13.60   $13.60   $13.60  
  7 purchase totals = $1,267.24       $1,394.2070   $1,394.21   $1,394.25   $1,394.30