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 $99.88   6.393%   $106.2653   $106.27   $106.25   $106.30  
  Purchase #2 $232.72   11.636%   $259.7993   $259.80   $259.80   $259.80  
  Purchase #3 $115.61   5.305%   $121.7431   $121.74   $121.75   $121.70  
  Purchase #4 $137.69   9.217%   $150.3809   $150.38   $150.40   $150.40  
  Purchase #5 $33.39   10.464%   $36.8839   $36.88   $36.90   $36.90  
  Purchase #6 $194.33   5.840%   $205.6789   $205.68   $205.70   $205.70  
  Purchase #7 $159.40   11.834%   $178.2634   $178.26   $178.25   $178.30  
  7 purchase totals = $973.02       $1,059.0148   $1,059.01   $1,059.05   $1,059.10