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 $59.25   11.740%   $66.206   $66.21   $66.20   $66.20  
  Purchase #2 $181.88   5.826%   $192.4763   $192.48   $192.50   $192.50  
  Purchase #3 $106.80   10.573%   $118.092   $118.09   $118.10   $118.10  
  Purchase #4 $176.81   11.659%   $197.4243   $197.42   $197.40   $197.40  
  Purchase #5 $53.29   12.871%   $60.149   $60.15   $60.15   $60.10  
  Purchase #6 $111.33   12.554%   $125.3064   $125.31   $125.30   $125.30  
  Purchase #7 $93.66   8.563%   $101.6801   $101.68   $101.70   $101.70  
  7 purchase totals = $783.02       $861.3341   $861.34   $861.35   $861.30