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 $185.68   13.772%   $211.2518   $211.25   $211.25   $211.30  
  Purchase #2 $142.36   8.591%   $154.5901   $154.59   $154.60   $154.60  
  Purchase #3 $75.55   12.213%   $84.7769   $84.78   $84.80   $84.80  
  Purchase #4 $35.34   3.317%   $36.5122   $36.51   $36.50   $36.50  
  Purchase #5 $81.70   7.425%   $87.7662   $87.77   $87.75   $87.80  
  Purchase #6 $168.52   3.847%   $175.003   $175.00   $175.00   $175.00  
  Purchase #7 $246.50   8.862%   $268.3448   $268.34   $268.35   $268.30  
  7 purchase totals = $935.65       $1,018.2450   $1,018.24   $1,018.25   $1,018.30