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 $195.29   8.306%   $211.5108   $211.51   $211.50   $211.50  
  Purchase #2 $34.86   12.440%   $39.1966   $39.20   $39.20   $39.20  
  Purchase #3 $84.32   5.455%   $88.9197   $88.92   $88.90   $88.90  
  Purchase #4 $83.28   8.253%   $90.1531   $90.15   $90.15   $90.20  
  Purchase #5 $157.25   11.144%   $174.7739   $174.77   $174.75   $174.80  
  Purchase #6 $237.28   12.557%   $267.0752   $267.08   $267.10   $267.10  
  Purchase #7 $156.54   8.513%   $169.8663   $169.87   $169.85   $169.90  
  7 purchase totals = $948.82       $1,041.4956   $1,041.50   $1,041.45   $1,041.60