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 $62.54   6.483%   $66.5945   $66.59   $66.60   $66.60  
  Purchase #2 $111.87   13.599%   $127.0832   $127.08   $127.10   $127.10  
  Purchase #3 $114.99   8.538%   $124.8078   $124.81   $124.80   $124.80  
  Purchase #4 $244.59   13.120%   $276.6802   $276.68   $276.70   $276.70  
  Purchase #5 $184.67   7.510%   $198.5387   $198.54   $198.55   $198.50  
  Purchase #6 $189.44   11.282%   $210.8126   $210.81   $210.80   $210.80  
  Purchase #7 $142.31   7.779%   $153.3803   $153.38   $153.40   $153.40  
  7 purchase totals = $1,050.41       $1,157.8973   $1,157.89   $1,157.95   $1,157.90