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 $202.81   6.151%   $215.2848   $215.28   $215.30   $215.30  
  Purchase #2 $247.52   8.721%   $269.1062   $269.11   $269.10   $269.10  
  Purchase #3 $124.55   10.502%   $137.6302   $137.63   $137.65   $137.60  
  Purchase #4 $109.66   11.414%   $122.1766   $122.18   $122.20   $122.20  
  Purchase #5 $163.74   4.466%   $171.0526   $171.05   $171.05   $171.10  
  Purchase #6 $118.40   4.489%   $123.715   $123.72   $123.70   $123.70  
  Purchase #7 $30.32   6.571%   $32.3123   $32.31   $32.30   $32.30  
  7 purchase totals = $997.00       $1,071.2777   $1,071.28   $1,071.30   $1,071.30