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 $84.90   12.239%   $95.2909   $95.29   $95.30   $95.30  
  Purchase #2 $189.25   9.145%   $206.5569   $206.56   $206.55   $206.60  
  Purchase #3 $242.30   13.363%   $274.6785   $274.68   $274.70   $274.70  
  Purchase #4 $59.93   7.755%   $64.5776   $64.58   $64.60   $64.60  
  Purchase #5 $102.85   4.258%   $107.2294   $107.23   $107.25   $107.20  
  Purchase #6 $168.85   12.645%   $190.2011   $190.20   $190.20   $190.20  
  Purchase #7 $180.97   11.260%   $201.3472   $201.35   $201.35   $201.30  
  7 purchase totals = $1,029.05       $1,139.8816   $1,139.89   $1,139.95   $1,139.90