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 $52.66   13.460%   $59.748   $59.75   $59.75   $59.70  
  Purchase #2 $224.38   7.373%   $240.9235   $240.92   $240.90   $240.90  
  Purchase #3 $170.89   4.748%   $179.0039   $179.00   $179.00   $179.00  
  Purchase #4 $131.26   5.728%   $138.7786   $138.78   $138.80   $138.80  
  Purchase #5 $240.76   5.509%   $254.0235   $254.02   $254.00   $254.00  
  Purchase #6 $96.41   13.701%   $109.6191   $109.62   $109.60   $109.60  
  Purchase #7 $160.96   3.869%   $167.1875   $167.19   $167.20   $167.20  
  7 purchase totals = $1,077.32       $1,149.2841   $1,149.28   $1,149.25   $1,149.20