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 $244.95   7.774%   $263.9924   $263.99   $264.00   $264.00  
  Purchase #2 $189.81   8.438%   $205.8262   $205.83   $205.85   $205.80  
  Purchase #3 $61.25   13.835%   $69.7239   $69.72   $69.70   $69.70  
  Purchase #4 $116.73   7.815%   $125.8524   $125.85   $125.85   $125.90  
  Purchase #5 $142.47   9.395%   $155.8551   $155.86   $155.85   $155.90  
  Purchase #6 $11.82   4.309%   $12.3293   $12.33   $12.35   $12.30  
  Purchase #7 $32.90   9.426%   $36.0012   $36.00   $36.00   $36.00  
  7 purchase totals = $799.93       $869.5805   $869.58   $869.60   $869.60