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 $164.39   13.707%   $186.9229   $186.92   $186.90   $186.90  
  Purchase #2 $73.48   5.256%   $77.3421   $77.34   $77.35   $77.30  
  Purchase #3 $77.70   9.332%   $84.951   $84.95   $84.95   $85.00  
  Purchase #4 $74.60   5.255%   $78.5202   $78.52   $78.50   $78.50  
  Purchase #5 $42.76   4.807%   $44.8155   $44.82   $44.80   $44.80  
  Purchase #6 $131.79   4.102%   $137.196   $137.20   $137.20   $137.20  
  Purchase #7 $137.65   5.521%   $145.2497   $145.25   $145.25   $145.20  
  7 purchase totals = $702.37       $754.9974   $755.00   $754.95   $754.90