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 $63.52   3.753%   $65.9039   $65.90   $65.90   $65.90  
  Purchase #2 $231.43   13.613%   $262.9346   $262.93   $262.95   $262.90  
  Purchase #3 $119.61   3.703%   $124.0392   $124.04   $124.05   $124.00  
  Purchase #4 $169.71   3.733%   $176.0453   $176.05   $176.05   $176.00  
  Purchase #5 $234.66   6.158%   $249.1104   $249.11   $249.10   $249.10  
  Purchase #6 $22.34   9.826%   $24.5351   $24.54   $24.55   $24.50  
  Purchase #7 $151.91   13.446%   $172.3358   $172.34   $172.35   $172.30  
  7 purchase totals = $993.18       $1,074.9043   $1,074.91   $1,074.95   $1,074.70