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 $146.69   13.567%   $166.5914   $166.59   $166.60   $166.60  
  Purchase #2 $67.52   6.320%   $71.7873   $71.79   $71.80   $71.80  
  Purchase #3 $216.68   10.537%   $239.5116   $239.51   $239.50   $239.50  
  Purchase #4 $201.80   10.779%   $223.552   $223.55   $223.55   $223.60  
  Purchase #5 $39.74   12.391%   $44.6642   $44.66   $44.65   $44.70  
  Purchase #6 $11.44   6.120%   $12.1401   $12.14   $12.15   $12.10  
  Purchase #7 $244.95   3.387%   $253.2465   $253.25   $253.25   $253.20  
  7 purchase totals = $928.82       $1,011.4931   $1,011.49   $1,011.50   $1,011.50