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 $191.25   12.562%   $215.2748   $215.27   $215.25   $215.30  
  Purchase #2 $186.75   10.498%   $206.355   $206.36   $206.35   $206.40  
  Purchase #3 $110.94   10.335%   $122.4056   $122.41   $122.40   $122.40  
  Purchase #4 $250.98   12.344%   $281.961   $281.96   $281.95   $282.00  
  Purchase #5 $205.77   8.572%   $223.4086   $223.41   $223.40   $223.40  
  Purchase #6 $34.74   3.645%   $36.0063   $36.01   $36.00   $36.00  
  Purchase #7 $74.41   8.737%   $80.9112   $80.91   $80.90   $80.90  
  7 purchase totals = $1,054.84       $1,166.3225   $1,166.33   $1,166.25   $1,166.40