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 $54.55   13.491%   $61.9093   $61.91   $61.90   $61.90  
  Purchase #2 $131.88   8.644%   $143.2797   $143.28   $143.30   $143.30  
  Purchase #3 $241.81   12.767%   $272.6819   $272.68   $272.70   $272.70  
  Purchase #4 $151.90   3.609%   $157.3821   $157.38   $157.40   $157.40  
  Purchase #5 $6.51   10.465%   $7.1913   $7.19   $7.20   $7.20  
  Purchase #6 $176.68   4.312%   $184.2984   $184.30   $184.30   $184.30  
  Purchase #7 $190.76   11.141%   $212.0126   $212.01   $212.00   $212.00  
  7 purchase totals = $954.09       $1,038.7553   $1,038.75   $1,038.80   $1,038.80