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 $162.41   12.435%   $182.6057   $182.61   $182.60   $182.60  
  Purchase #2 $161.56   11.734%   $180.5175   $180.52   $180.50   $180.50  
  Purchase #3 $250.82   12.690%   $282.6491   $282.65   $282.65   $282.60  
  Purchase #4 $90.68   8.695%   $98.5646   $98.56   $98.55   $98.60  
  Purchase #5 $211.28   11.409%   $235.3849   $235.38   $235.40   $235.40  
  Purchase #6 $113.32   11.709%   $126.5886   $126.59   $126.60   $126.60  
  Purchase #7 $106.63   11.450%   $118.8391   $118.84   $118.85   $118.80  
  7 purchase totals = $1,096.70       $1,225.1495   $1,225.15   $1,225.15   $1,225.10