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 $68.96   8.156%   $74.5844   $74.58   $74.60   $74.60  
  Purchase #2 $245.37   3.402%   $253.7175   $253.72   $253.70   $253.70  
  Purchase #3 $192.97   6.722%   $205.9414   $205.94   $205.95   $205.90  
  Purchase #4 $71.60   5.575%   $75.5917   $75.59   $75.60   $75.60  
  Purchase #5 $70.36   9.437%   $76.9999   $77.00   $77.00   $77.00  
  Purchase #6 $173.27   6.236%   $184.0751   $184.08   $184.10   $184.10  
  Purchase #7 $230.44   12.449%   $259.1275   $259.13   $259.15   $259.10  
  7 purchase totals = $1,052.97       $1,130.0375   $1,130.04   $1,130.10   $1,130.00