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 $196.49   11.695%   $219.4695   $219.47   $219.45   $219.50  
  Purchase #2 $100.69   8.850%   $109.6011   $109.60   $109.60   $109.60  
  Purchase #3 $64.85   3.523%   $67.1347   $67.13   $67.15   $67.10  
  Purchase #4 $78.26   11.606%   $87.3429   $87.34   $87.35   $87.30  
  Purchase #5 $141.30   8.640%   $153.5083   $153.51   $153.50   $153.50  
  Purchase #6 $228.87   12.454%   $257.3735   $257.37   $257.35   $257.40  
  Purchase #7 $12.80   8.133%   $13.841   $13.84   $13.85   $13.80  
  7 purchase totals = $823.26       $908.2710   $908.26   $908.25   $908.20