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 $236.50   13.385%   $268.1555   $268.16   $268.15   $268.20  
  Purchase #2 $177.65   13.571%   $201.7589   $201.76   $201.75   $201.80  
  Purchase #3 $108.40   7.493%   $116.5224   $116.52   $116.50   $116.50  
  Purchase #4 $11.80   5.822%   $12.487   $12.49   $12.50   $12.50  
  Purchase #5 $86.61   11.207%   $96.3164   $96.32   $96.30   $96.30  
  Purchase #6 $38.39   5.489%   $40.4972   $40.50   $40.50   $40.50  
  Purchase #7 $190.55   8.109%   $206.0017   $206.00   $206.00   $206.00  
  7 purchase totals = $849.90       $941.7391   $941.75   $941.70   $941.80