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 $184.38   11.297%   $205.2094   $205.21   $205.20   $205.20  
  Purchase #2 $49.32   7.335%   $52.9376   $52.94   $52.95   $52.90  
  Purchase #3 $147.47   4.126%   $153.5546   $153.55   $153.55   $153.60  
  Purchase #4 $217.51   5.865%   $230.267   $230.27   $230.25   $230.30  
  Purchase #5 $245.43   4.194%   $255.7233   $255.72   $255.70   $255.70  
  Purchase #6 $172.58   3.367%   $178.3908   $178.39   $178.40   $178.40  
  Purchase #7 $246.40   12.645%   $277.5573   $277.56   $277.55   $277.60  
  7 purchase totals = $1,263.09       $1,353.6400   $1,353.64   $1,353.60   $1,353.70