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 $241.42   11.607%   $269.4416   $269.44   $269.45   $269.40  
  Purchase #2 $248.85   7.428%   $267.3346   $267.33   $267.35   $267.30  
  Purchase #3 $196.43   8.200%   $212.5373   $212.54   $212.55   $212.50  
  Purchase #4 $69.62   9.623%   $76.3195   $76.32   $76.30   $76.30  
  Purchase #5 $97.42   13.735%   $110.8006   $110.80   $110.80   $110.80  
  Purchase #6 $39.66   13.770%   $45.1212   $45.12   $45.10   $45.10  
  Purchase #7 $201.74   7.632%   $217.1368   $217.14   $217.15   $217.10  
  7 purchase totals = $1,095.14       $1,198.6916   $1,198.69   $1,198.70   $1,198.50