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 $10.25   10.847%   $11.3618   $11.36   $11.35   $11.40  
  Purchase #2 $163.97   5.589%   $173.1343   $173.13   $173.15   $173.10  
  Purchase #3 $168.51   12.811%   $190.0978   $190.10   $190.10   $190.10  
  Purchase #4 $139.30   3.706%   $144.4625   $144.46   $144.45   $144.50  
  Purchase #5 $24.87   3.493%   $25.7387   $25.74   $25.75   $25.70  
  Purchase #6 $74.38   10.574%   $82.2449   $82.24   $82.25   $82.20  
  Purchase #7 $204.48   11.528%   $228.0525   $228.05   $228.05   $228.10  
  7 purchase totals = $785.76       $855.0925   $855.08   $855.10   $855.10