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 $57.94   11.577%   $64.6477   $64.65   $64.65   $64.60  
  Purchase #2 $206.80   6.741%   $220.7404   $220.74   $220.75   $220.70  
  Purchase #3 $95.59   8.139%   $103.3701   $103.37   $103.35   $103.40  
  Purchase #4 $187.85   8.710%   $204.2117   $204.21   $204.20   $204.20  
  Purchase #5 $163.48   7.866%   $176.3393   $176.34   $176.35   $176.30  
  Purchase #6 $10.48   12.701%   $11.8111   $11.81   $11.80   $11.80  
  Purchase #7 $151.76   13.486%   $172.2264   $172.23   $172.25   $172.20  
  7 purchase totals = $873.90       $953.3467   $953.35   $953.35   $953.20