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 $61.38   3.514%   $63.5369   $63.54   $63.55   $63.50  
  Purchase #2 $80.92   11.469%   $90.2007   $90.20   $90.20   $90.20  
  Purchase #3 $28.72   4.720%   $30.0756   $30.08   $30.10   $30.10  
  Purchase #4 $228.98   6.254%   $243.3004   $243.30   $243.30   $243.30  
  Purchase #5 $223.60   7.766%   $240.9648   $240.96   $240.95   $241.00  
  Purchase #6 $228.66   7.600%   $246.0382   $246.04   $246.05   $246.00  
  Purchase #7 $194.33   7.385%   $208.6813   $208.68   $208.70   $208.70  
  7 purchase totals = $1,046.59       $1,122.7979   $1,122.80   $1,122.85   $1,122.80