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 $116.27   12.758%   $131.1037   $131.10   $131.10   $131.10  
  Purchase #2 $68.94   12.184%   $77.3396   $77.34   $77.35   $77.30  
  Purchase #3 $185.97   8.858%   $202.4432   $202.44   $202.45   $202.40  
  Purchase #4 $102.75   8.718%   $111.7077   $111.71   $111.70   $111.70  
  Purchase #5 $91.43   7.812%   $98.5725   $98.57   $98.55   $98.60  
  Purchase #6 $204.97   7.437%   $220.2136   $220.21   $220.20   $220.20  
  Purchase #7 $153.74   13.789%   $174.9392   $174.94   $174.95   $174.90  
  7 purchase totals = $924.07       $1,016.3195   $1,016.31   $1,016.30   $1,016.20