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 $50.47   12.803%   $56.9317   $56.93   $56.95   $56.90  
  Purchase #2 $104.98   12.625%   $118.2337   $118.23   $118.25   $118.20  
  Purchase #3 $15.67   6.337%   $16.663   $16.66   $16.65   $16.70  
  Purchase #4 $24.62   8.478%   $26.7073   $26.71   $26.70   $26.70  
  Purchase #5 $163.90   8.841%   $178.3904   $178.39   $178.40   $178.40  
  Purchase #6 $188.75   12.835%   $212.9761   $212.98   $213.00   $213.00  
  Purchase #7 $19.74   13.121%   $22.3301   $22.33   $22.35   $22.30  
  7 purchase totals = $568.13       $632.2323   $632.23   $632.30   $632.20