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 $164.51   13.491%   $186.704   $186.70   $186.70   $186.70  
  Purchase #2 $121.82   11.769%   $136.157   $136.16   $136.15   $136.20  
  Purchase #3 $209.34   11.704%   $233.8412   $233.84   $233.85   $233.80  
  Purchase #4 $142.47   10.595%   $157.5647   $157.56   $157.55   $157.60  
  Purchase #5 $181.31   12.400%   $203.7924   $203.79   $203.80   $203.80  
  Purchase #6 $111.52   13.181%   $126.2195   $126.22   $126.20   $126.20  
  Purchase #7 $44.86   7.734%   $48.3295   $48.33   $48.35   $48.30  
  7 purchase totals = $975.83       $1,092.6083   $1,092.60   $1,092.60   $1,092.60